That's a point I had overlooked about the level authority gradient, that the captain in the right seat can be slow to detect or react to deviations. It's so, and I agree that makes for a higher level of risk.
One factor there is perhaps that a RHS captain's comments are more 'loaded' than an FO's, more of a challenge, so that one is slower to make a comment from the RHS. Mainly though, a captain is lacking in specific FO skills.
In our company relatively few people are qualified in both seats but every so often some trip comes up when we have run out of FOs for some reason or other.
I find that flying in both seats in the sim is a good way to learn things about CRM that are otherwise just theory. Of course one could question whether an hour with a normal crew composition is of more value than an hour with a captain/captain crew. I suppose that is the case.