If you have to hit a direction on your controlstick as a modifier for strikes, that means you can't move in any direction while trying to input for said strike.
The fact that they separated different strikes entirely from left stick inputs allows you use omni-directional footwork while striking. It's the same reason they removed swaying from the left stick.
Though the button scheme is somewhat complex, there is no other way to do it. There are too many different stand-up techniques and not enough buttons to map them all. Stacking modifiers is the only way to get it done. Unless you want to automatically do different strikes depending on the distance between the fighters (like how you knee instead of pushkick when you're close).