IMO TP is there to simulate a stamina stat. This is not to say everything you are saying is not true. But it does make sense that in a longer fight we would run out of stamina as we dodge, attack and do all of this in heavy armour. But as it stands there is no variation on TP you get 1000 and that is it. However, if stats were more relevant they could have given TP buffs based on stat placement or an even better idea would be to drop in TP materia for melding into gear. At least that would give crafted gear some relevance at end game. Even TP potions and food would be acceptable. But to say everyone has the same TP is odd. Perhaps this was a decision made for reasons of class balancing.