Actually he's doing nothing wrong... Keyboards can't accept more than 3 simultaneous key presses and in some cases even 3 are too many...
That being said theres nothing that can'l be done about that without reducing the number of hold types...
As for Hitbox Controllers... that just takes some getting use to... I think one of the mistakes people make one trying to do moves like
or
is they actually try to press those buttons at the exact same time like this
and thats just a recipe for disaster. Really I think what we're supposed to be doing is overlapping the inputs... first press
and keep it held down then press
...
Its going to be abit trickier for Diagonal Inputs but the principle remains the same... first press
and
and make sure their both held down before you press
and you should be fine....
The down side to playing this way is you won't be able to play KOF or Guilty Gear...