What Burd said. Only casters that really run out of MP for AOEs are healers. Casters never have to deal with that problem. Also, a punishment for death isn't TP, it's, you know, death. You die and you get weakness, lose your gauge, uptime. Also, once you use Invigorate and never die again, you'll never worry about TP. Changing TP to what it is in SB was needed because it was simply unfun to run out of TP because you've been playing well, but now it's on the other side of the problem; it doesn't feel like it even exists unless you die or AOE. Even when it comes to AOEs, melee resources are far inferior to melee, and objectively worse than casters, who have almost infinite resources.

On the question on what TP does in PVP: It acts as a resource and replaces the CD for skills like Quick Reload and Jump so it'd be used more often at the cost of TP. Exactly how Shinten works right now, for example.