The removal of TP

TP honestly served only one purpose, limiting AoE on the physical classes. Weaponskill combos generally ate TP equal to the regen, and thus were effectively free.
Really the same purpose it served would be done by adding a MP cost to AoE skills.


Cross-class skills
The Role actions are kind of a reworked version of that idea. It's not quite the same and certain combinations did go away but they didn't just remove the system... Also, certain cross-class skills were more required than others, so you only had so much to work with when it came to customization...


Greased Lightning
The biggest problem with Greased Lightning was that it was an unavoidable loss of DPS as you had to build up the stacks at the start of a fight, and if you at any point during a fight had controls disabled by them fancy mid fight scenes or something you lose the GL and had to rebuild it lowering your DPS simply because you're playing MNK.
The best you can do to minimize this is Perfect Balance to throw out 4 Snap Punches...