Why do we have 1000 TP? Would it be better if we had 100?

[Risvertasashi]

Honestly it's just as arbitrary as any other number. Why specifically X MP or HP? As with TP, the importance isn't its absolute value but its relation to other values (cost of a spell vs total mp pool vs regen ticks... % of HP a big attack removes, a heal spell restores, etc).

Ultimately, 1000 is a nice round decimal number. 100 is very intuitively 10% of 1000, which then gives people an intuitive feel for how much of their resource pool they're using.

Cost of spells increases with levels too, so honestly I'm not sure why they don't just make MP a fixed number that only gear can affect...

Actually, the switchover in FFXI wasn't bizarre. Rather, it was LONG overdue.

For ages, methods for building up TP have depended heavily on fractional amounts of TP. With the three-digit TP bar, these values were always rounded down visually and it made it a chore to work out just how effective things that boosted your TP gain were. Multiplying everything by ten, the value of equipment and abilities that fractionally boosted TP became much more apparent.

In FFXIV, I'm guessing that they made it a four-digit number anticipating that sometime in the future there might be need for finer granularity in TP gain/usage.

A potential example: A job ability for a future job that halves TP consumption for all party members for fifteen seconds. Now, what are you going to do about abilities that cost 7 TP in a three-digit model...

Also, this. ^