a) What Jaspers of Earth 238 did -which is the equivalent of arguing with a What If as evidence
b) What future timelines showed he is potentially capable of - however with no account of how he got from his proven level to this future potential capacity, using it as a reference for his definitive capabilities is illogical.
Granted his suggested capacity marks him as the most powerful of the mutant reality warpers, Jaspers has never actually done anything on panel to justify his hype.
While I agree that MJJ is, in most cases, vastly overrated, I don't think CK has demonstrated feats suggestive of being able to overcome his powers/warp.