Smash games are very different from each other though. Other fighting games have really similar fundamentals, but I ****ing suck at Brawl for example. Not that I'm amazing at 64 or anything, but I don't understand how to win a Brawl match honestly.
M2K said something interesting on his AMA. Someone asked him if Isai could be the best at Melee if he came back or something along those lines. M2K said he'd be a top player, but probably not the best because he has a "don't get hit" mentality and too many 64 specific habits, whereas M2K would always consider getting hit and DI'ing the right way.
I think if we were to make parallel comparisons, boom is better at 64 than leffen is at Melee. It's hard to say because the relationship between the top players in Melee is different from the ones in 64. We've never had a tournament with players like Isai, Boom, Jouske, Moyashi, Gerson, Alvin in it.