I honestly think that mega medicham should stay in B+
Now don't get me wrong, he has the raw power up the arse, but that's not all that it takes to succeed. Whenever I use him, there are a few main things that always trouble me:
1. No bulk
2. Sub-par Speed
3. No good boosting move
4. Sub-par typing
5. Mediocre Priority
His lack of bulk especially hurts. He can't take any strong neutral hit without dying for the most part, and he always dies to any decent SE hit. He has no reliable recovery to mitigate this, and his psychic/fighting typing still leaves many resistances to be desired. Being practically a free switch-in to aegislash is never really a good thing, especially because he can KS everything you have while scouting for random fire punch.
100 base speed is cool, but there is just too much at that benchmark atm. When he's so easy to revenge kill and KO with several pokemon, (like talonflame, or any strong user above 100 base speed with neutral STAB) he really doesn't ever pose a problem.
To compliment his fantastic ability and decent speed tier, he possesses absolutely no decent set up moves to utilize. Bulk up is your only real option, and you're definitely not a good bulk up user when you get OHKO'd by every aegislash out there. Any lack of long-term presence really hinders this guy, he isn't really gonna be cleaning much anytime soon.
His mediocre priority is also a pretty big problem. Fake out + Bullet punch is a powerful combo, but you lose way too much coverage just trying to fit those in. Bullet punch alone, even with adamant max investment, is pretty disappointingly weak. You can't rely on it to pick off too many decent threats.
When I see a wallbreaker, I immediately try to classify it into a bulky one or a fast one. An example of a fast one would be Landorus, Keldeo, or Mega Pinsir. All hit a great speed tier of over 100 and have strong moves to back up their bark. Slower ones include stuff like Aegislash, Azumarill, and Bisharp, which have great typing, and then good bulk or a really strong priority, along with power to back all of this up.
Mega Medicham does not have bulk, a super strong priority, or a great speed tier to back up his great power. He deserves to stay wherever he is.
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Tbh these are problems Y-zard also has, the only exception being it has good special bulk.
Y-zard's typing is arguably better but it leaves it with a quad weakness to stealth rock meaning it almost always has to be used as a lead. 78/78 physical defense is also pretty bad, nearly as bad as Medicham.
252+ Atk Life Orb Bisharp Sucker Punch vs. 0 HP / 0 Def Mega Medicham: 208-246 (79.6 - 94.2%)
252+ Atk Life Orb Bisharp Sucker Punch vs. 4 HP / 0 Def Mega Charizard Y: 224-265 (75.1 - 88.9%)
252+ Atk Choice Band Talonflame Brave Bird vs. 4 HP / 0 Def Mega Charizard Y: 288-340 (96.6 - 114%) -- 81.3% chance to OHKO
Neither of them are tanking much. Y-zard also has that nasty Rock weakness, and Stone Edge is a really common coverage move. Its special bulk is really good but the meta is mostly physical anyway, though it is a plus in Y-zard's favor since it allows it to (barely) survive things like Mega Manectric's Thunderbolt.
100 base speed, for a wall breaker, is completely passable. That's Y-zard's speed tier, too. You outspeed every defensive mon bar speed-invested Latias (and Zapdos, if you count a speed tie) and neither of them are switching in to Ice Punch if they're that invested in speed. And I mean, realistically, what mons are there between Mega Medicham's speed and Mega Pinsir's? Garchomp, Lando-T, Thundurus-I, that's everything relevant to OU. You don't risk speed ties with base 100's but that is again only a handful of threats. The reason why I support Medicham going to A- is because, with the banning of Mega Lucario who had a
much better speed tier than Mega Medicham, there is no longer a mega that completely outclasses Medicham. Mega Pinsir, Y-zard, X-zard, there's not as sanic fast as Lucario was, their base speed is the same or comparable to Mega Medicham's.
IMO being easy to revenge kill is not a good argument for something's tiering. It's
really easy to check something, it's counters that really matter and Mega Medicham is terribly short on them. Good scarfers like Garchomp and Terrakion check nearly every S and A rank mon. Talonflame revenge kills nearly everything,
including Mega Pinsir. There's also the issue of, if you're being forced out by a revenge killer, you've already KOed something. And, as a wall breaker, what you KOed could have been a wall, opening up a sweep for a fellow teammate. That's really what wall breakers are for, not sweeping but supporting other teammates by getting rid of pesky walls and defensive cores.
No good boosting move? You already OHKO or 2HKO the entire game sans ultra niche stuff like Sableye, why would you want to boost, especially if you're liable to get checked by a switch in you could have KOed? Aegislash is not that safe a switch in anyway, with a predicted Fire Punch, or especially with a Medisharp core where you can end up getting pursuit trapped or giving a free turn to Bisharp.
Priority moves: Y-zard doesn't need them. Kyu-B doesn't need them. Mega Garchomp doesn't need them. Keldeo, Terrakion, they don't need them. Medicham doesn't really need them, either. Priority moves are almost entirely useless for a dedicated wall breaker. All of them are very low BP (with the exception of Sucker Punch and Talonflame's Brave Bird) and are completely ineffective against walls.
Also Medicham technically does have reliable recovery in the form of both Recover and Drain Punch, but both are ultra shitty moves to run when your main goal is to wall break.
