Let's put it this way:

I'm a Ninja. I Mutilate x number of times over a fight. Mutilate costs 80 TP.

You are also a Ninja in my same party. You run out of TP a few times over the course of a fight, so you get off 2 less Mutilates because you are waiting for TP ticks and can't reapply it right away, and of course you don't want to clip it because that would be dumb. This means you spend 160 less TP on Mutilate, but since we are in the same fight and swapping Goads like the awesome Ninja brethren we are, that means you have 160 more TP for other, non-Mutilate things. What do you spend that 160 TP on that gives you as much damage as 2 Mutilates do?

The answer is you don't, because the Ninja doesn't possess any attacks that both cost TP and do as much damage per TP spent as Mutilate. It's not just how much TP you spend, it's what you spend it on. That is why in practice haste can lead to a dps loss, because you use too much Aeolian Edge and not enough Mutilate.

I say again, theoretically and even in practice with merely decent play, haste is a DPS increase or at worst neutral. But to say spending 1000 TP in 3 minutes is the same as spending 1000 TP in 4 minutes, or to say it doesn't matter when you spend it, is to neglect the fact that some abilities are limited more by time than they are by TP.