For me you're kind of using the same language as in a penalty try. "Would he have definitely won?"
If the race had been red flagged and restarted? No, not definitely.
If the race had been restarted with Max behind the lapped cars? No, not definitely.
If the safety cars rules had been fully followed at the end once some lapped cars went past? Yes, definitely. This is the issue here because if the wording is correct and it had been followed correctly then the race would have ended under the safety car. Yes there might have been a sudden mechanical malfunction or an absolutely huge, rookie error by Hamilton behind the safety car, but that would be like disallowing a clear penalty try because the player might have dropped it at the last moment.
I think everyone is in agreement that Masi has royally ****** up. Question is how and should it be resolved off track? For me yes. I'll admit I'm biased towards Hamilton, but that call blatantly favoured Max and from my reading of the rules, broke the rules. I get that you say Max might deserve it because of incidents like when Bottas took him out. However, those are normal incidents that are part of racing. That's luck. Bottas definitely didn't intend to take Max out, he just ****** up big time and was punished for it. However this called clearly favoured one driver over another and a championship shouldn't be decided that way. Ending under a safety car is unlucky for Max, but he was going to lose anyway without it. He only won because of a dodgy decision by the officials.