How does one define properly challenging?
Does it provide feedback on the challenges? Does it teach the requisite mechanics or is the player at the mercy of trial and error?
The solution should at least attempt to be more apparent to the player than the glitches. If one is able to find the bosses blindspot via geometry exploits the player shouldn't even know about general play sooner than they can find his weakspot, then the game might not be overly informative that a weakspot even existed or was too punishing for the processes of finding it. Basically the difference between running QA tests and actually playing the game for enjoyment. When the former becomes an easier method, I think pause should be given
I've known games that I can make this criticism of. Not saying Risen 2 is or will be one, as that's speculation beyond my comfort zone.
But then again, I'm not the type to think game master and players are in a state of confrontation, either.