SSBM is hardly all about wavedashing. I'll list out the main differences between SSB64 and SSBM (Being an SSBM pro player, you can look up XIF on YouTube if you want, I play peach)
SSB64 is really about landing the first hit and 0-deathing your opponent. Directional influence (influencing where you fly off to after getting hit) is alot more primitive in SSB64 than SSBM, along with other tactics to help survival, such as meteor cancelling, ledge teching, etc. I think this quote about MVC2 fits SSB64 nicely, which is "Mindgames exist until the first hit lands"
SSBM is more about character specific strategies than anything. This is obviously important in SSB64, but for the most part every character has a bread and butter death combo vs almost everyone, whereas in SSBM it varies radically. Falco needs to press the advantage he has on stage and mobility control with his laser. He can effectively control his space and limit the mobility of other characters all with his laser. In some cases this lack of mobility really hurts the opponent, and allows Falco to do his own brand of bread and butter death combo. Someone like Jigglypuff in contrast is more about preventing the opponent from entering her own space, along with the best edgeguarding strats in the game, and against some characters really easy rest combos and opportunities. Marth once again differently is about safely approaching using his massive range and priority.
SSB64 is more character balanced while less fundamentally balanced, while SSBM is less character balanced but more fundamentally balanced. This sounds weird I know but the basic idea is that while in SSB64 there are tiers (no denying Pikachu, Kirby, and Ness are the best) every character has a fairly good chance at winning (Well... Samus sucks). In SSBM, if you're not playing Fox, Falco, Marth, or Sheik you really stand little chance of getting first at the national level. You'll see Peach, Captain Falcon, Ice Climbers, jigglypuff, and even a ganondorf or two sneak up there, but its mainly the top four. The issue is that certain tactics in SSB64 are simply overpowered/underpowered to an extreme point. In SSBM, there is really no tactic like that where spamming it or always going for it will always yeild neutral or positive results.
Case in point is Sheilding in SSB64. Its near useless because of the amount of stun you get. The sheild breaker in this movie is hardly unheard of. Matter of fact with kirby against any character, you can land one uptilt and you have an auto sheild break which they cant escape because of the stun. 3 up tilts to forward smash and you have instant sheild break. Another case being grabbing, where the throws are so absurdly powerful for kills, yet grabbing has almost no startup or wind down. SSBM has certain powerful tactics, but none to the point where you cannot be punished at least sometimes. Power shielding can disrupt falco's lasers, ledge teching to ledge hop attacks against people who camp the ledge and go for spikes, going for weak spots on powerful attacks to counter like peach's d smash, etc. The only really overpowered tactics in SSBM is basic reflector strats with Fox and Falco, but even then there are times where foolish use can lead to death.
As for Isai: He loves SSB64, and hence why he plays it so much and is so good. He mildly enjoys SSBM but doesnt take it nearly as seriously. Which is why you'll see him lose matches sometimes and then other times seem unstoppable. My Melee teams partner beat Isai in tournament pools, but that just happens. He also played isai in SSB64 and barely took a stock per match >_>
/rant about a game I like too much >_>