Why do assassins, a class that's supposed to do BURST damage, consistently have the most dmg overall

Again this class is supposed to deal BURST damage to HIGH PRIORITY targets. Why are they consistently doing HIGH burst damage and HIGH sustained damage? I consistently see these champs in EVERY freaking game and then they do the most damage in EVERY FREAKING GAME.

They're WAY too safe. They do WAY too much damage. They have WAY too much mobility. They have FAR too much CC (Ekko has two slows and a fucking stun to go along with a movement speed buff and two dashes....................). STOP OVERLOADING THE MOST BRAINDEAD CLASS AND MAKE THEM TAKE ACTUAL SKILL AGAIN.