This is all fine and good but facts remain.
Note that of what you list, below, only 1 point is an actual "fact".
1. Bossy's peak is significantly below Hull's.
I probably agree that Hull's peak (obviously 1989-90 to 1991-92) is a bit above Bossy's, but "significantly"...? I don't see it. Going by the ever-flawed Hockey Ref.'s top "adjusted points" seasons:
Bossy
108, 106, 97, 95, 93, 93, 92
(One of Bossy's "93" seasons was while missing 13 games.)
Hull
118, 97, 95, 88, 86, 86, 86
(Hull's "97" season was while missing 7 games.)
So, in the 7 best seasons, Bossy beats Hull in every one except for the 1st position.
Hull has a definite edge in peak goal-scoring, but I'd say that's easily compensated by Bossy's vastly better ES results. Now, obviously, you have to apply era/team context to that (a straight comparison is clearly unfair to Hull), but still, it's pretty jarring when Hull's top three seasons are at +20 (two of them being 'minuses'), while Bossy's top three seasons are at +162.
Both were great in the playoffs. Like, all-time greats.
So, maybe at peak, Hull has a slight edge...? But if he does, it's
very close and certainly not by a "significant" margin.
2. Bossy never went above 3rd in Hart voting, while Trottier routinely finished higher than him.
This is an interesting and seemingly substantial point. Hull's peak-season Hart finishes are 1, 3, 3, while Bossy's big two are 2, 4.
But here's the thing: In 1981, 1982, 1983, 1984, 1985, and 1986, Bossy outscored Trottier every year, sometimes by large amounts. Yet, as you note, he never finished higher than 3rd in Hart voting. Trottier got there first, and was the kind of two-way forward voters at that time loved. In 1982, Bossy had 14 more goals than Trottier and almost 20 more points, and yet the Hart votes were 41% for Trottier and 11% for Bossy. Do you think that was probably quite accurate, or is that more so votes being split down the middle and old voters preferring the old-school player? (On a related note, has anyone ever had a worse Hart finish for a spectacular season than Bossy in 1978-79? He had 69 goals, 126 points, went +63... and finished 7th in Hart voting. Tough crowd!)
What I'm pointing out is that it's actually harder (esp. if you're not a physical center in that old-school era) to rack up big Hart votes when you're on a Dynasty team. For comparison, consider that Denis Potvin never won a Conn Smythe, but Butch Goring, Ron Hextall, and Ryan O'Reilly all have. It's about relativity.
And, as I noted before, Hull was in a "perfect storm" situation in 1991 to win his Hart. If you roll the dice five times, maybe he wins that one once. If Gretzky wasn't in his 12th season, he'd have been over Hull in voting. If Lemieux had played 70+ games, he'd have been over Hull. And, most notably, if Adam Oates hadn't gotten injured mid-season, he'd have outscored Hull on the Blues. If Oates had put up 150 points or whatever that season (thus becoming the 5th player in history to do so), the votes for Hull would now be split with him (as the Trottier / Bossy votes were often split).
So, I dunno. Full marks to Hull for his epic 1990-91 season, and I do think that one season of his is probably (?) better than any season Bossy ever had. But I don't think his Hart win is really that significant in this comparison.
3. Bossy is often named (a) the greatest Islander, (b) the greatest goalscorer of all time, and (c) even a Top 10 player of all time. Not on this forum but there is life outside HFBoards as well.
There may be people on Long Island who say this, but I've heard / read of a single hockey fan ranking Bossy that high. Certainly not a top-10 player of all time!