That would be equivalent to the skill point level up systems of EQ/FF11/ or more modern-ish the talent system of WoW.

As always it can get complex, and while not bad, not always good, because you're charging developers with a task that they probably don't want at this point in time. Constantly balancing things to avoid cheat characters/builds.

That's the original reason they considered scrapping physical levels. It spun out of their control to balance classes.

Static stats are far easier to deal with obviously, but if people want the developers to ride that horse...well it's a rough ride.