If Corbyn did what he did, he was stupid,
100% he did. Whether he said what he was accused of saying is another matter.
Yes, groping is more serious than calling someone a 'stupid woman'. An admission, and apology would have sorted things.
While not an expert lip-reader, I know enough to tell that what he said did not match his claim that it was "stupid people", and it may well have been "stupid woman".
However, to come back and lie to Parliament (which is what he appears to have done) is more serious than calling Mrs May a stupid woman.