Why tanks deals that much damage??

Full tank malphite with 30k dmg,like WTF?One shot adc?And hes unkilable?I dont understand this meta at all. Every game i have malphite in game he does most or second most damage in game.Not one game,not two games,EVERY GAME!Not full ap malphite,legit full tank malphite with only tank items.How can malphite solo carry a game?He had most damage taken and almost most damage done(second to my adc) Will tank meta ever end?Or at least make it that tanks cant do that much damage,lower their base dmg or something. Not to mention that malphite now counter fiora in lane(cause of that comet) and that was one of the easiest matchups for me. Did anyone else noticed how much dmg tanks do? Sorry for my grammar :)