Reasoning for removal of TP, but not MP?

[Shurrikhan]

Just from browsing through the classes: every class which relied on TP as their main resource is now your standard "Press the button when off CD without having to think further" whereas MP classes still need to calculate their resources.

Why the glaring difference?

Because they could save time that way but apparently didn't think they could get away with then removing MP in the same sweep, especially since it is still at least a tiny bit relevant to healers.

Basically, unless you spammed your AOE skills there were never any risk of running out of TP, so it was in essence a pointless resource.

It'd eventually run out without Invigorate. Like a caster DPS runs out without Lucid Dreaming, but without the stat that increases the need for either CD (SpS/SkS) being quite so hated as among non-BLM casters. They were effectively identical. Both could essentially strap their CDs to auto-clickers and forget resources exist.

All TP did was force a commitment in dungeon runs with full pulls. If not everyone AoEed or otherwise performed at least kind of competently, those who were AoEing would run out of TP before everything's dead, and then you'd probably wipe. Of course, the same can still be said about the interactions of competent DPS and tank CDs so it's not like that's been outright removed. It's just a bit less glaringly obvious.