Found out a new property of DKs smashattacks (well, got it from japanese framedata pages):
They all have some sort of "trample"!
Let me quote my description of it:
"Trample: This is an attribute some moves have that let's them continue to go on even when they clash / clank. They then also proceed to hit the other character since their hitbox continues normally. They can still be outprioritized to get beaten completely, and since (normal) aerials can't clank they also "ignore" this property."
Though before you get too excited, it seems like DKs usmash won't hit opponents after they clashed (this only matters against opponents on a platform above you anyway though).
Fsmash seems weird too. Sometimes it happens to hit the opponent, but most of the time it doesn't. Could be hitbox / spacing dependant. But DKs hurtbox on his arms while he reaches forward is really bad for him since they don't have a hitbox at first which makes it super easy to hit him out of it.
Dsmash works well though. It always beats moves and then hits the opponent as well.
I guess I should use dsmash more.