Yeah, Deoxys-S/Xurkitree using Zap Cannon are what makes me think that it should be banned. Against Deo-S, you have to switch-ins except Groudon, Zygarde (hoping it doesn't run Ice Beam), Blissey (which can be broken through with Nasty Ploy and Focus Blast), Zapdos, or some really bulky mons like Giratina and Cresselia (but if they're too passive then they can be set up on with Nasty Plot). You have to be really cautious when switching in an offensive check because they could get severely crippled. For Xurkitree, you have to switch in a Ground or Electric type mon, OR you could switch in a faster offensive mon (with a great prediction). Blissey doesn't really stop it cause of Tail Glow, and Groudon could get put to sleep with Hypnosis.
Zap Cannon just seems so unnecessary to me. Every mon that gets it also gets Thunder. Thunder is 10 points weaker and is 70% less likely to paralyze. Zap Cannon was given 50% accuracy to be balanced, but Pidgeotite fucks that up.
Even though the Zap Cannon + Dynamic Punch combo isn't prominent in gen 7 mnm, because of the hitting yourself in confusion nerf of 50% → 33%, I still think it could be a slight problem. I actually haven't seen it myself, but I did see
thesecondbest's comment on it, so I want to give it a try. I'm gonna try out Pidgeotite Deoxys-Defense with Zap Cannon/Dynamic Punch/Psycho Shift/Recover. I have 2 accounts in the top 10 ladder of mnm, so hopefully I can make a splash with this set.
You forget about [insertmonhere] running Sceptilite, which is completely immune to Zap Cannon. Jirachi is a good choice, as it isn't weak to common Ice or Fairy coverage from Zap Cannon mons, even with the added dragon coverage.
To be frank I don't see what the problem with Zap Cannon is from your argument but rather with the excellent coverage certain Pidgeotite mons have. Also I don't believe you should be looking at 'walling a move' when you try to get a move banned, but rather look at common users of the move to see if they are broken. I personally have not heard any complaints about Xurkitree or Deoxys-Speed (before this) or Mew and Pidgeotite Genesect is generally considered the inferior set. In my personal experience I have found them rather easy to deal with.
Xurkitree: Except for the perfect accuracy sleep, which you (read, I, because I suck) generally have to fodder off to sleep clause, Xurkitree cannot kill SpD Pdon, while Pdon slaughters it back.
+3 252+ SpA Xurkitree Energy Ball vs. 248 HP / 252+ SpD Groudon-Primal: 333-392 (82.6 - 97.2%) -- guaranteed 2HKO (note that Modest is probably not the best nature)
0 Atk Groudon-Primal Precipice Blades vs. 0 HP / 0 Def Xurkitree: 542-642 (176.5 - 209.1%) -- guaranteed OHKO (keep in mind No Guard makes P Blades never miss)
I'm tempted to say that nothing that's walled by Pdon is going to be easily banworthy.
Deoxys-Speed:
So I asked in the om room what speed to run and they said max speed for Pidg Xurk on webs and Geoxern so that's what I'm calcing it with.
0 Atk Groudon-Primal Precipice Blades vs. 0 HP / 0 Def Deoxys-Speed: 226-267 (93.7 - 110.7%) -- guaranteed OHKO after Stealth Rock
252 SpA Deoxys-Speed Focus Blast vs. 248 HP / 252+ SpD Groudon-Primal: 119-140 (29.5 - 34.7%) -- guaranteed 3HKO after Stealth Rock
Another win for Pdon... even with Nasty Plot, that doesn't turn into a OHKO.
Your set doesn't seem to include a Psychic STAB? I'm actually kinda confused as to what the set you're talking about is. I went with Nasty Plot / Zap Cannon / Ice Beam / Focus Blast. Without Focus Blast Blissey walls, and Pdon deals with it no matter what, unless it has Psychic AND Psychic Terrain is down on the field.
Genesect:
Better off doing -Ate shenanigans, I can calc if you like.
Mew:
Mew does basically the same thing as Deo-S but with a better movepool and 5 higher SpA but much lower speed. I can calc it too with whatever moves you like, but Pdon walls.
Thunder being a weaker replacement is completely irrelevant as a competitive argument.
Basically what I think your point boils down to is not Zap Cannon being broken on its own but Pidgeotite allowing multiple somewhat broken moves to work, most importantly sleep. I'm neither the best nor the stalliest of Mix and Mega players, but I don't believe that if there is a problem here that it is Zap Cannon. I suggest that you look at either Pidgeotite sleep, Pidgeotite itself, or the abusers of the move, because most mons that get of Zap Cannon are perfectly balanced, if annoying.
Also:
[10:47:31]
#Chloe:Pidgeotite will not be banned
[10:47:37]
#Chloe:Zap Cannon will not be banned