In the Beginning Was the Word, and the Word Was Suck: A Guide to Truenamers

[Psyren]

If your GM allows Gate, he deserves what he gets.

FTFY

If your regard a class feature you get at level 20 as a key section of a class, then you play a different type of D&D then I do (to borrow an expression by Zaq).

I have currently a level 12 truenamer. He is doing fine. Of course, he doesn't have much in terms of competition: the party members are: a Samurai, a Ninja, a Monk and a Healer, all single classed, all level 12...

The specific classes don't matter as much as (a) the challenges they face and (b) the gap between them. A group like that might struggle through a premade or challenge campaign, but if the DM is tailoring the obstacles to them they will do just fine. Nobody is really in a position to totally outshine anyone else.