The problems with the current system in my eyes are:
- The current system puts balanced setups at a disadvantage because it is more effective to either focus the physical or the magical armor portion.
- Low damage CC strong skill trees like Hydro and Aero are less effective than damage heavy Pyro and Geo, with which you can blow all the shit up.
- If everything is predictable, it is less of a fight and more of a puzzle game. It feels less like a CRPG.
- Every mage can now take a warrior skill and use its CC with full efficience. In DOS1 you needed the right stats to increase success chance, now you don't. Which kind of makes skill hoarding even more likely.


Your idea would even enforce focus based team and skill hoarding even more. Either all will need to have the same kind of skill set, or all will have pretty every skill, to chain up those elemental reactions. With only 4 AP one char alone can hardly profit from such a system.