Yea, I don't think the agony mechanic is too large a barrier. But it is nonetheless a direct, linear and bimodal addition to the game which did not exist at the time release. Agony is even a progressive system. This is was stated flatly in Anet's blog on the agony mechanic in fact.
The actual point at which agony kicks in isn't too relevant to the fact GW2 introduced a multi-mode, tiered advancement system what is currently separate from other PVE activities. A bimodal, linear and progressive play system.
I only put the caveat of "is was not bimodal" in the original post as a matter of accuracy within the rules of the game.