well 1) i dont make poor builds
but on topic, my point with the DR feats and a 22base con is that without those (lets say 12base con)....the barbarian is much much easier to kill.
on its own, pure barbarian lvl 40 only gets 10/- DR...not too significant, i believe a lvl 9 dwarven defender gets 9DR? which is just as close....9lvls vs 40.
and without a high con, that barbarian (in this example) loses 200life. 200less life and almost half the amount of DR should he avoid the high con price and 3epic feats.
now if you want to discuss how the beneficial effects of DR increase exponentially as you increase the amount of DR, we can (actually no i dont want to, i dont want to get into the math of it)...but my point is just that to become this beastly tank the barbarian has to invest in a lot...or else he is nothing special.
im just trying to defend this because i know of some severe weaknesses that can destroy the barbarian...thus i dont think its overpowered.