The only things that could be considered OP when merging is things that would wipe your TP when switching (I think sachets might do that, but I'm not sure ^^. I can see them not wanting to combine those for that reason (The other things should be able to be combinable though). However, if we take a look at the C. Staff, they took off a lot of the extra enhancements (like damage down, etc...), so if these are combined, I could see the effects becoming slightly weaker.