Marcelo plays butterfly's so do a ton of others. I don't actually think Marcelo walks around that much lighter than you by the way... The smaller the weight class, the more time they tend to have spent in guard in general, but that's not a knock on butterfly guard. I think its actually a great guard game for heavier weight classes.
One thing though, while I do think pretty much everyone can play some sort of game from butterfly guard, limb length isn't really an advantage while playing it. Any closed guard variation, especially a rubberguard, would be a little easier for longer legged guys than shorter legged guys.
Shorter legged guys usually find it easier to bring butterfly's in and out and such though...
Hope this kind of answered your question, but its working for you and is a good guard game... I'd keeping doing it. Don't fall into the trap of "I like butterflys but I'm "SUPPOSED" to be better at such-and-such based on my body type". Just build your own game, its like your fingerprints and will be unique anyway.