To kick things off, I'd like to thank everyone who's participated in this thread (as well as the UU ladder!) so far. This has easily been one of the most active suspect tests I can personally recall and, in spite of a bunch of points I personally disagree with, there have been a lot of many solid arguments from both sides. Personally, I'll be voting
Do Not Ban on Mega Venusaur. Many of my reasons to do so have already been addressed by other users, so here are some aspects that I'd like to add on top of those:
Mega Latias vs. Mega Venusaur
Throughout this thread, there have been a lot of mentions to prior suspect tests, and how Mega Venusaur is unique in the sense that it is currently being tested over its defensive prowess, with Mega Latias being the only Pokemon in UUBL that can be directly compared to the situation at hand. At the time, I was one of the biggest supporters of a Mega Latias ban, and if that Pokemon got suspect tested again under similar conditions, I'd still be doing the same with little hesitation. My pet peeve with Mega Latias was the fact that the versatility of its Calm Mind set gave people way too little room to adapt, be it in the teambuilder or in an actual match against it. Offensive Calm Mind with 3 Attacks, 2 Attacks with Roost where you could be facing any combination of Draco Meteor, Dragon Pulse, Psyshock, Psychic, Ice Beam, Thunder(bolt), Surf, Hidden Power Fire and Mono Attacking sets with Reflect Type, Substitute, Refresh, Roar (it wasn't common at the time of the test, but I think it would've grown to become a menace with Spikes support) were all viable, and all of them had vastly differently answers (although it is true that some of those overlapped and some teams could get away with less insurance against this Pokemon). That coupled with Latias' supportive options turned it into a Pokemon that wasn't just, as many people used to call it, a "breath of fresh air for balance": it was (to me), a legitimate toxic presence to the UU metagame.
Now, if we attempt to directly compare Mega Latias and Mega Venusaur, it is possible to conclude that Mega Venusaur lacks this ability that Latias did to adapt to Pokemon that are commonly used to beat it. The standard 3 Attacks + Synthesis set has very little room for change aside from Hidden Power Fire, since dropping Sludge Bomb leaves it completely open to Moltres, Latias and a lot of Fairy-types, and I'm sure as hell you don't want your Venusaur to lose to Water-type Pokemon. If you do decide to ditch Hidden Power Fire, Scizor now becomes a lot more menacing, Cobalion can set up on Earthquake-less variants and so on. It is true that moves like Knock Off, Sleep Powder and Leech Seed are very good under the right circumstances, but it is very rare for Venusaur to actually be able to afford dropping any of its staple moves. Growth Venusaur is a set that I have used a lot throughout this test, and my final verdict is that (excuse me for the profanity) it fucking blows. When Mega Venusaur originally dropped, my belief was that the only way it'd turn out to be broken was if its set up sets were good in this metagame. However, Venusaur's 4MSS makes Growth a lot worse than it sounds on paper. Dropping Synthesis was something I tried at first, but the inability to take on threats you'd usually be able to switch into is very ugly. Overall, I'd say that Growth's only advantage is capitalizing on shakier answers to this Pokemon, such as Blissey (and even then, keep in mind that stall teams currently use Pokemon such as Crobat and Haze Tentacruel), but it doesn't really match up any better against balance and bulky offense than standard sets do. Swords Dance and Curse are two Mega Venusaur variants which can definitely work, but between the Scald weakness, lacking a significant way to deter Pokemon such as Moltres and Crobat from switching in on it and the reduced longevity due to not having Giga Drain mean that these two sets play exactly the same role as Growth Venusaur: capitalizing on people who run overall shakier answers to it. The real point I'm trying to get to here is that no matter how much you mess around with this Pokemon's moves, it is very unlikely that you stumble upon significant ways of mitigating the impact of match ups that could be considered bad to Venusaur. Crobat still stops Growth, Swords Dance and Curse variants, Moltres suddenly becomes even more menacing if Sludge Bomb is ever dropped, Kommo-o does great into any variant that lacks Curse (and even then, it still possesses a decent chance of coming out on top), nukes still hurt is as much and so on (refer to
pokeisfun's list if you want more examples). Moving onto the next point:
Using Viability Ranking Placements as a major argument against Mega Venusaur
I'll be blunt with this one: this was probably my least favorite aspect of this thread by a large margin, and I'll try my best to explain why that is the case. I'm one of the current hosts of the thread in question, and I did maintenance on it almost on my own for almost a whole year before other people accepted to shoulder the burden in my stead. As a concept, this thread's goal is to separate Pokemon in categories depending on a plethora of factors, with one of those factors being how the Pokemon interacts with other threats in the UU metagame. When you consider that the thread has barely been updated to account for Mega Venusaur's existence, it is only natural that you will find some of the best Pokemon at dealing with it way lower than they should be. Besides that, there's a world of subjectivity involved in the making of those, and many people will do things differently. Some of us use particular Pokemon more or less regardless of their rank. For example, I slap Moltres around on my teams as if it is comfortably sitting in S Rank, and it works for me. Last but not least, and while this may sound bad at first, I do believe that it is completely fine for people to be using Pokemon that aren't particularly stellar in order to deal with Mega Venusaur. If you think about it, a metagame works more or less like an ecosystem, and I feel like there are way too many "I don't want Mega Venusaur in UU because it forces me to use Toxicroak, Salazzle, Dragalge and other "bad" Pokemon" posts. Pokemon become better and/or worse in a metagame depending on how their niche raises/drops in demand. A good example of this is Gastrodon jumping up to OU from PU despite being barely viable in the tiers between those two. Is it a top notch Pokemon? Not really, but people were in need of answers to threats such as Tapu Koko and Heatran, so it started receiving more usage up there. What I'm trying to get across here is that we shouldn't be blinded nor guided by which letter the Pokemon we need to use to stop Venusaur are sitting below in the VR thread when it isn't even like the Pokemon in question are only useful for that particular niche. I fully believe that our tier has the necessary tools to adapt to this Pokemon's presence in a way that isn't unhealthy.
Banning "Unhealthy" Pokemon and Smogon's Tiering Philosophy
I won't delve too deep into this for one simple reason: I don't think Venusaur is unhealthy to the tier. However, I am of the personal opinion that Smogon as a whole should aim to make its formats reward the better player the vast majority of the time, and this means that aspects of the game/Pokemon should be looked into regardless of whether or not they are able to 6-0 teams with very little counterplay as long as they interfere with balance in a significant way. Alolan Ninetales was once banished under this reasoning. Weavile's prowess as a Pursuit trapper was a major argument towards its eventual demise and I'm sure that you could find more examples by delving deep enough into Smogon tiering. This is not all too relevant to this suspect test in particular, but I've seen some people claim that only offensive behemoths get banned, so it's never bad to remind users that this isn't the case at all.
---
To finish this post, I'll reiterate two of my favorite points that have been brought up by other users: firstly, the fact that Mega Venusaur's answers can be bossed around by entry hazards and Pursuit trappers is probably the most compelling argument towards a potential ban. Being able to outlast the Pokemon that are supposed to handle it is obviously huge. However, I do not think that this is always the case, considering that Pokemon such as Kommo-o are resistant to both Pursuit and Stealth Rock and that all of Crobat, Moltres and Latias have access to Roost to last through moves that get thrown their way. Lastly, Mega Venusaur itself is incredibly weak to many indirect ways of counterplay. Burns, paralysis, entry hazards, weather among others are all awful for this Pokemon, and I do not think that is it mandatory for all Pokemon to have definite and reliable counterplay. A good example of this is how threatening Mamoswine is to a vast majority of UU teams, yet you hardly see it winning games on its own, with chip damage and proper prediction usually playing a major role in the match up against teams with this Pokemon. To me, Mega Venusaur is a similar case of a threat that doesn't truly have a vast quantity of counters or checks, but still ends up being manageable most of the time.