In Avengers: Endgame Thanos single-handedly takes on

the Hulk, Thor, Iron Man, Captain America, Captain Marvel AND hands it to each and every one of them, KO'ing the Hulk, breaking Captain America's shield, breaking Iron Man's armour (twice), nearly killing Thor with Stormbreaker, beating Captain America half to death, catching Mjolnir mid-air, punching Captain Marvel (in)to the ground and killing Loki (a god).

Also, he did most of this BEFORE getting any of the Infinity Stones.

So, what gives? What makes this character so powerful?