honestly all they need to do is just bring back TP for melees. A system where there is a direct consequence for your actions speaks louder than any difficulty curve. Spamming your aoes on just one or two mobs? Too bad now you have no TP. Spamming just your ranged attack? Too bad now you have no TP. Caster's get penalized for dying but not melees? The fact that you can go through the entire MSQ from ARR to EW, only spamming your aoes as a tank should worry the FFXIV devs. Though it would make for an awkward video compilation. "Can you clear FFXIV with only Overpower"?

However, they also need to introduce an incentive system with the TP. For example, let's say you do your 123 rotation, each costing 100 TP respectively. First action will cost the full amount (100 TP), the second will be 50% (50 TP), and the last will be free (0 TP). Players can actually visualize and see that if I do my combo rotation correctly I don't lose a lot of TP for playing correctly. It would also instinctively teach them to always complete your combo rotation.