How would a true historical event that is not flattering to Muhammad, even get passed along by devout believing Muslims who would rather reject it and dismiss it?
Wouldn’t that leave us with historical records that got marked as being weak(er) because no Muslim wanted to preserve something that is unpleasant?
Do we have strong isnads for hadith from non-Muslim sources? Are any highly esteemed narrators in these chains, non-Muslims?
If we don’t have such, then we cannot rule out he unpleasant narrations from a historical perspective. What survived and is deemed ‘reliable’ is understandably then, going to have a very strong pro-Muslim bias that would tend to discard unpleasant events.