I would say "Trump won only because Russia interfered in the election" is a direct, explicit claim that the election was illegitimate. I'm not saying I disbelieve it or that I believe the current claims of fraud, but there is a clear equivalency here.
Saying that Russian hacking influenced the election is demonstrably true. Whether it caused Trump to win is not. I don't remember anyone actually saying that Trump would not have won without Russia, though I could be wrong about that. This is still a big difference between that and calling millions of votes, lawfully cast, as illegitimate. Do you seriously not see the distinction between the two?
I don't see the distinction you're making. There are plenty of differences between the two scenarios, but "only one of those is a claim that the election is illegitimate" is not one of the differences IMO.
