I don't see the purpose of such thought experiments as being to model reality (we've already got a perfectly good actual reality for that), but to simplify it. Hypothesizing omnipotent beings and superpowers may not seem like simplification, but it is in one key aspect: it reduces the number of variables.

Reality is messy, and while we have to deal with it eventually, it's useful to consider simpler, more comprehensible models, and then gradually introduce complexity once we understand how the simpler system works. So the thought experiments arbitrarily set certain variables (such as predictive ability) to 100% or 0% simply to remove that aspect from consideration.

This does give a fundamentally unrealistic situation, but that's really the point - they are our equivalent of spherical cows. Dealing with all those variables at once is too hard. In the situations where it isn't and we have "real" situations we can fruitfully consider, there's no need for the thought experiment in the first place. Once we can understand the simpler system, we have somewhere to start from once we start adding back in the complexity.