No it's not, going "full ******" is a fool's errand. But remember the lessons learned in Tropic Thunder, you never go Full ******. Full ****** is aiming for an un-achievable AC for areas that you don't need AC anyway (Epic).
Finesses build = bad idea 99% of the time (that freak who solo'd VoD and a few other fit that 1%). You do not have to be a finesse build to get usable AC where AC still works. More on that in a second . . .
You're right about HP though, going from 400-500 HP on my evasion mook's made a world of difference in those situations where you have tot take a hit.
There's two kinds of high-level monsters, epic and non-epic. Lets go with Elite Amrath which actually harder than any epic I've seen. The big difference between Epic and non epic-trash is non-epic trash actually fights back. In epic everything has such **** saves that they are either stunned or held and we pound on them when senseless. When they aren't helpless, they swing VERY SLLLLOOOOOOWWWWLLLLYYY so you'll either have time to get out of the way or heal yourself before they swing again. AC in epic simply isn't needed because we have other exploits (yes, I said it) to mitigate the incoming damage. Non-epic content it's still useful which is what 95% of the player play.
Keep in mind, epics are only played by 5% of the population. The "real" endgame of DDO is TR-grinding and it that the Dex build would be fine.