Yes, the problem isn't that the definition isn't 100% formal. If "autism" meant "unusually sensitive to loud noise" (and presumably other symptoms get new labels) that would be reasonable. But it seems to mean "unusually sensitive to something OR unusually methodical OR unusually bad at reading emotions OR unusually affected by other's emotions OR ... ", and almost nobody has every symptom, but two people may have completely different symptoms while a third person has some from each.