I think this is the correct answer.So I think that's true - but that it's up to the league to run it's own affairs - which includes its own constitution and by-laws.
So if the league wanted to amend its own constitution to remove the 50 mile rule it's free to do so.
If the league however just wanted to pretend the 50 mile rule didn't exist and put a team in Hamilton without consent ot Toronto / Buffalo - I think there's a good chance of a lawsuit. It wouldn't be under competition law however, just under plain-old breach of contract.
It's worth noting however (and some people already have) that the NHL is an extremely small and exclusive club. There are only 32 owners, many have been in the league for decades, and they meet multiple times per year. There's zero chance that a majority of the league decides to say "screw the Leafs - we're going to put a team in Toronto no matter what they say". That's probably double true when you consider MLSE ownership in Bell and Rogers give hundred of millions of dollars to the league every year. You just don't screw over your colleagues and business partners like that.
I'm amused that Americans somehow think that Canadian courts are bound by American anti-trust law. It doesn't apply here.