So if it had the same techniques and physics (I think people are just reading the title lol)... I agree, Project M would not have had as much reason driving it into existence. It probably would have not even be inspired in the first place due to lack of kindling, so to speak. I could have seen there being a 'just go play Melee if you want Melee' ideology to the subject of why the game is not as fast.. Even if Project M did come into being, it would be much less backed, like Brawl Minus is currently. Also, I think Melee would not have as large of a community as it does today, because this version of Brawl would be more inviting to the competitive Melee players and so you have more of them making a transition to it. Melee would definitely still be around, just smaller than it is now in our reality.
Moving on, Smash 4 may have been what, in our reality, Brawl was to Melee. Sakurai, wanting to make it more of a party game, introduces tripping, makes the game slower, and probably some other things we wouldn't like. We all get pissed, so we make Project B (I guess this is in the future when we are modding Wii U games). Project B is pretty much our reality's Smash 4 but with the players controlling what happens. Characters cut between Brawl and Smash 4 would be re-introduced. Lots of interesting stuff happens.