1. You could do it in the air, but holding down a direction prevents you from doing the HP+HK movement in general, so for example, when holding down, you can't call an assist, hence the one frame problem.
2. Out of what I've seen, that's not really true? Previously I had to hit specifically U, F, D, B (or in any starting position) and not any of the diagonals until I changed the code to have that 8-way leniency (Using the $(direction) option). Similar situation with the half-circle into 3p, but that's more a personal issue since the game needs to detect the release of back first which isn't a problem for controllers ofc, but is for keyboard.
or maybe i have a skill issue lol