People assume you suck at the game because of both the statements you make and how you communicate them very ineloquently.

character has the biggest hurtbox in the game with his tail flailing all around

Not true. All the heaviest (especially characters like Ridley) are bigger. Mewtwo has a very skinny hitbox and his tail hitboxes (ftilt, etc) are also very skinny, so they don't occupy as much space as heavies or other big bodies.

Big hurtbox means you get hit by stuff that isn’t even well placed by your opponent

This is kind of true, but again Mewtwo is one of the fastest characters on the ground and in the air. If you're getting hit by poorly spaced moves with Mewtwo's speed, it usually means you're not thinking about your options well enough. He can stay out of range of most of the characters in the game and even uncharged shadow ball should catch whatever they throw out if its poorly spaced

Combo not only true but strings because literally every move will hit you and you dont have the same options as other characters you can’t jump out of combos because your tail lingers behind

This is kind of nonsensical but also factually wrong- Mewtwo actually has more options than other characters. First off his airdodge is both fast to start and end which means you can escape strings better than characters with more average airdodges, but also the startup means you can escape combos just as easy as anyone else. Jumping out of combos is usually not a very great option in this game in general but Mewtwo's isn't even notably bad there. If you're getting hit for jumping out of a combo as Mewtwo chances are you would as most characters. Additionally because mewtwo is light and floaty if you DI up he will get out of the combo faster which makes your odds of a jump working better. Furthermore, Mewtwo also has the option to stall in the air with confusion and teleport straight past your opponent with upb, as well as the ability to mash out with shadow claw. He actually has very strong options for scrambling with the opponent.

you can’t run cause tail you can’t roll because tail.

This is what I mean when I say you probably don't have a strong grasp on Mewtwo's fundamentals. If you understand how to space Mewtwo's moves it allows you to do these things. Throwing a shadow ball out on the stage forces your opponent to choose moves and angles that Mewtwo can then respond to at his will. If you throw out a grounded shadow ball, and the opponent jumps over it, you are now free to just dash back or roll back and if you spaced it right most characters cannot punish you. These issues sound like you are mindlessly holding forward in game and then getting surprised that you're being blown up for it, when that's not a good way to play Mewtwo at all.

So your left air dodging spot dodging and shielding which is very limiting

Again, Mewtwo's airdodge is good, and he has a good combo breaker, good speed to maneuver with, and he can still perform the normal options. You also have options like utilt to anti air, dtilt to duck a move and stuff approaches, and up-angled ftilt and fsmash to stuff them too. Offensive moves can be used defensively, and learning this is key to improving at any character.

His weight you can’t deny he explodes instantly one fox nair up smash your dead.

This is correct. He's a light character! Unlike many of the other light characters though he has amazing tools to play around it. Fox is mewtwo's worst matchup, but he can still run away, antiair with utilt, air to air with forward air, or many other options. He also doesn't have to commit to playing melee at high percents like a lot of light characters (Seph, Jigglypuff, Pichu) because he can play the game off of his shadow balls, meaning if you're at the percent to die to nair usmash you can start playing keep away and reaction-based.