Exenterator's effect duration does not vary with TP.

[Creelo]

Evasion is important and relevant to all end game content in this game :P
On a serious note, you won't notice any difference whether the effect is on or not, for 95% of content.

I never stated it was.

But for times when the effect does matter, even if it is for that "5% of content," I'd rather the duration just stay at 90secs and not be needlessly nerfed. :/