I don't know what's the parent's problem, but "this assumes x holds true" is actually much more clear and straight-forward, which really helps to stay on track

I don't know what's the parent's problem, but "this assumes x holds true" is actually much more clear and straight-forward, which really helps to stay on track with the discussion. At the very least it allows the opponent to ask if there's something available w/o this assumption, which "you have bigger problems" barely does.