Dorukan's defenses did hold out. Xykon and Redcloak couldn't breach them, and they were stuck there for months. Even after defeating Dorukan himself, they still couldn't get past the sigil, and while Xykon had figured out what he needed to do to unlock the Gate he still didn't succeed. I'd say Dorukan's defenses worked fine. By comparison, Serini's defenses have only held for a much shorter time so far, although it remains to be seen whether they too will be breached.