AGI has a twofold impact on your overall evasion
I don't know where you heard this. But it is not true.
first AGI vs DEX check and then the added evasion it gives.
The AGL vs Dex check determines critical hit rate.
Considering a level 90 THF has an evasion skill of 361 capped (unmerited) in addition to 48 evasion from traits, and you stack on another 17 skill from Boxer's Mantle and Evasion Torque plus 27 evasion from assorted gear that lands you at 453 evasion. Granted this is in no way a huge amount, it is to the point where I've seen AGI doing extremely well in boosting the actual evasion.
2 AGL is no different than a piece of gear with 1 evasion on it. The cap is the cap. Once you reach the (very easy to reach at 90THF) cap, you will not evade more than the cap. It doesn't matter what stat you apply.
We most certainly have more than +48 from traits as well. I don't know of anyone that has bothered to test at what level but we have gotten at LEAST one more level of evasion bonus since the level cap raise. If not 2.
I have a MONSTEROUS evasion set. But its really only for show. I do use it for ichi casting sometimes, ***** moments, kiting, pulling etc etc. But for the most part, GH + 2x evasion Kila's (if I'm soloing/lowman) caps me (with some variation) on just about everything I fight.