To be clear I have no experience with fighting games. With that out of the way this is how I would approach the problem.
Mechanically sticks are actually 4 switches:
Down
Right Left
Up
The only way you can trigger diagonal inputs is to trigger two perpendicular switches. That means that for 
, both 
and 
are true. This is why just holding worked in your bp.
In Street Fighter for example: for the dragon punch ( + p) , and are also valid. It’s because the combination of 3 inputs , and are true within a given time. And since is true within 
you can even 
+ p and will count as valid.
There are also games like Street Fighter 3 that only expect + p and don’t allow shortcuts. It’s up to what you want.
It’s not that simple.
Curious to see how far Input Combos (Enhanced Input) will take you. Using Street Fighter as an example: when right is forward i can + p for a skill, but (other player crosses) + p is also valid because at the moment of the input both and were forward. This leads me to believe that what is buffered are not literal inputs, but commands created in a given context.
If Input Combos can be made to work like that then awesome!