Well, I for one am super glad it was fake. Smash trailers are fun because when they start, they get you guessing. They build up to the character and play on your anticipation. I recall being very confused when Mega Man got killed as my brain quickly scrambled trying to figure out who used a harpoon only to realize it was Ridley's tail just moments before he showed himself. And Dedede's savage prank wouldn't have had me laughing so hard if it didn't put so much time into slowly amping up my expectations
I'm not a Castlevania fan, but had he not been leaked, I could easily see myself being very confused and then having an "Aha! It makes so much sense now!" moment when his name splashed on screen, but instead I fealt almost nothing for that trailer because there was no surprise and it was for a character I didn't care much for. Now don't get me wrong, I'm really happy to see such a unique character make it in and he seems super fun to play, but my hype for him would probably be exponentially higher if that trailer had the impact it was meant to.