So to respond to
JoycapJoshST, and anyone else who intends to continue this discussion for him since Gary just laid into the guy:
Buzzwole's access to certain offensive options that Mega Heracross simply isn't enough to offset the sheer disparity in breaking power between the two. Mega Heracross's immense power (its Close Combat is approximately as strong as CB Buzzwole's Hammer Arm), Skill Link, and access to Swords Dance make it so that Mega Heracross is extremely self sufficient in punching significant holes in the large majority of the tier with just 3 moves in dual STABs + Rock Blast. Meanwhile, 4 moves is arguably still not enough for Buzzwole as it has to cover so much ground that its STAB moves cannot, especially since its Fighting STAB is unreliable and compromise its breaking power (walls either sponge its hits better or start outspeeding it), or make it susceptible or worse yet setup fodder for dangerous threats like Zards, Volcarona, Magearna, etc., which necessitates the use of these coverage moves even more.
Let's look at the moves Buzzwole has and would want in this meta:
- Superpower / Hammer Arm: Fighting STAB and strongest STAB, but undesirable side effects greatly prompt the need for backup moves to use
- Leech Life / Lunge: More reliable STAB, though its generally poor coverage and more importantly lesser power than the Fighting STABs (a problem not shared by Mega Heracross) still makes these more expendable. Though it hits Mew which Buzzwole otherwise can't touch.
- Ice Punch: while it seems like a nice advantage Buzzwole has over Mega Heracross in the Lando-T and Zygarde matchup,
not using this puts Buzzwole at risk of having the tables turned on it by SD Lando-T and Coil Zygarde, so now it looks like less of a bonus and more like a necessity for Buzzwole to even properly do its job at being a Ground check (MHera's access to SD makes it not as susceptible to those two)
- Poison Jab: admittedly, this can be nice for bulky Fairies like Tapu Fini, Clefable, and Azumarill but MHeracross's +2 Rock Blast already does significant damage to Tapu Fini and straight up cleaves through Magic Guard Clef and Azu. Meanwhile, Unaware Clef, Poison Jab's main target, is primarily found on stall teams, which have other members that can take on Buzzwole, notably Mega Sableye and Toxapex.
- Earthquake: Buzzwole's only chance at even phazing Toxapex in the slightest. Expect Buzzwole to contribute zero offensive presence against a Toxapex team otherwise. Also hits AloWak and Gengar.
- Stone Edge: You want this to not invite in the likes of Charizard, as well as prevent setup opportunities for stuff like Volcarona, Mega Pinsir, and Gyarados.
- Substitute: I omitted Focus Punch alongside this because Focus Punch conceals the fact that Buzzwole likes Sub not for allowing it to use Focus Punch, but because Buzzwole appreciates being behind a Sub in general. Not that it even makes use of this as well as Mega Heracross since Buzzwole's Fighting STAB is really unreliable for Sub: Superpower and Hammer Arm's stat drops conflict with Sub's staying power, while Focus Punch pretty much forces you to be behind a Sub to consistently work.
- Roost: grants Buzzwole recovery and lets it function like a consistent Ground check, as well as being one of Buzzwole's greatest niches over MHeracross. With that said, Ice Punch becomes mandatory for this as a result for aforementioned reasons and Fighting STAB because it pairs far better with Ice than Bug STAB, leaving only one moveslot open to cover potential threats.
Thought about ThunderPunch as it collectively covers Fighting-resistant Waters like Tapu Fini, Toxapex, Mantine, and Gyarados, but I consider this less useful since Buzzwole can hit them with other moves that also cover more significant threats, and ThunderPunch is debatably not even enough for Toxapex.
This isn't versatility; this is straight up 4MSS. Dropping even one of these moves hurts Buzzwole's niche and overall presence considerably, while Mega Heracross can sit back and still be able to pick and choose. The Z-moves also only really help Buzzwole even net kills in the first place, something MHeracross has far greater ease achieving: literally the only thing I can think of for Z-move Buzzwole to break that MHera has no chance against is Z-Poison Jab against Unaware Clef, and if you've read my aforementioned descriptions about Poison Jab's uses, you'll realize that you won't even reliably bait your target since the opponent has alternative answers. Buzzwole's offensive niche in this meta is incredibly strained, and it's safe to say that Buzzwole doesn't hold even a matchstick to MHeracross in the attacking department, forcing it to rely on its defensive niche which, while not as eclipsed by other alternatives, still leaves Buzzwole pretty overshadowed.
Btw, I also don't know where you got the impression that Buzzwole has a superior matchup against Celesteela: MHeracross takes only ~51% at the very most from defensive Celesteela's Flamethrower and OHKOes with +2 Close Combat, while Buzzwole needs ThunderPunch to even accomplish the feat of 2HKOing defensive Celesteela since its Fighting STAB's stat drops most definitely impede Buzzwole's ability to 2HKO Celesteela, and even then Celesteela can Protect itself out of TPunch's 2HKO range. The only scenario which I can imagine Buzzwole doing better than MHeracross against Celesteela is Choice Band Superpower vs offensive Celesteela after SR damage, and Choiced Buzzwole is an extremely shaky idea in this meta as its attacks are all risky to be locked into considering the sheer amount of setup threats in the tier that can take advantage of their resistances to Buzzwole's STABs or against its unSTAB moves, which makes Beast Boost almost useless.
Gary: unexcapetable -> unacceptable :P
