you haven't ran the calculations have you. a nasty plot shadow ball only dose 25% of a bulky steel arecues life and 50% ghost. while after a swords dance Arcues kills it with extreme speed or judgement.
These are not hpothetical situation when almost any pokemon with a nasty plot and over 360 speed, can kill any thing. aka Mega lucario. and if mega lucario is physical it can one shot it with adaptability bullet punch after swords dance. Mew two just ain't that great because it lack the of priorety moves and lack of defence witch is more important because there is pokemon with absolutly rediculous attack stats like mega mawile hitting it with super effective sucker punch.
Hell people are saying the most borken pokemon in ubers right now is power herb geomancy xerneus.
Also on the note fo lucario being OU is because people are just now learnng how broken adaptability Sp atk mega lucario is. And if you knew about the meta game you would know that he has 2 out of 3 aprovals for banning to ubers.
Or the Pokes with unaware who ignore opponent stat boost. im sorry there just to many poke that kill mewtwo. Even agislash is capable of killing it while seting up on it.
And lugia can just use amnesia like every single lugia dose and survive whileist healing to full hp.
Choice band talon flame also one shots mewtwo. ( well it has a chance to. mewtwo x is garentee though)
And i apologige for my text im in college now and im training my self not to double space as much. I hope this is better.
Lolno, No Mewtwo is going to be using shadow ball on steel arceus, that's why i mentioned Aura sphere, which does 50% to steel arceus without buffs. Arceus can't even kill mega mewtwo Y with an extreme speed that's sword danced, and Mewtwo responds with a 2hko by either a stab psystrike or a move to exploit his weakness/neutral damage. And Mawile is returns to uselessness if Mewtwo or anyone on his team brings will o' wisp
And no, mewtwo Y does not need any buffs to Put lucario down. Unless Mewtwo is sent in on a swords danced lucario that uses close combat or bullet punch on the switching in turn and the next turn, mewtwo Y will OHKO lucario with aura sphere before he can do anything, Mewtwo doesn't even need a set up.
Power herb xerneas would KO mewtwo unless mewtwo has enough special defense EV's in which case Mewtwo 2hko's xerneas. Not to mention A Power herb xerneas becomes a liability if the enemy team has a single pokemon with roar. Or taunt, which mewtwo can learn.
Just about every semi good mega is on it's way to an impulse ban to ubers, Mega lucario is no different. Mega mewtwo will still OHKO him in any situation he can attack at all, He is just plain outclassed by mewtwo.
Unaware doesn't matter, quagsire and clefable can't touch Mewtwo who can ko them without any need for stat boosts. Aegislash's gimmick is king shield and setup, if any smart player is using mewtwo he can easily predict what aegislash will do and respond with a shadow ball which 2hko's aegislash even in shield form. Or Mewtwo can just use taunt and laugh his arse off while obliterating aegislash's gimmicky strategy.
Mewtwo can still 3 or 4hko a Multiscale lugia without setup, and Can use calm mind while Lugia is using amnesia to the point where it matters little what the lugia or any other poke does due to a +4 Sp def and sp atk lucario making a gigantic hole in the opponent's team. Heck, taunt still applies here, with Mewtwo just taunting lugia and proceeding to destroy it while attacks bounce off.
And no, Talonflame can't OHKO Mewtwo Y even with Max attack and a choice band, Worst case scenario mewtwo still has 5% left and OHKO's talonflame with Psystrike.
Look, you're just arguing specific situations where you think Mega mewtwo can be trumped, but it doesn't matter because Mewtwo is still the Most powerful pokemon there is, He has the numbers on his side and likely always will. If there's a pokemon that will try to set up, Mewtwo will outspeed, Taunt, and destroy that pokemon. If it's unaware, It statistically cannot stand up to Mewtwo regardless.
tl;dr- mewtwo can taunt, enemy can't set up, if enemy doesn't set up, mewtwo can still destroy enemy. Mewtwo wins
Interestingly, while you're correct that it's never been said anywhere that Mega Mewtwo is the strongest, recent promotions for the Genesect movie (and even in the special Mewtwo: Prologue to the Awakening) stated regular Mewtwo as being "the most powerful Pokemon in the world", much like how Game Freak promoted Kyruem as "the most powerful Dragon-type Pokemon in the world". And if Mega Mewtwo X or Y are even more powerful than the original...
Yeah.
And also this.
(I thought i remembered Mewtwo being referred to as the most powerful pokemon, but not where/when it happened, thanks for this.)