Who said you can't have fun in a clan that ALSO accomplish things. At least in mine I make sure we all have fun, ni pressure into making collabs and we usually joke around with it everyday. The difference is that the members I have ACTUALLY animate for fun, and when we make collabs we all learn from eachother. We share files and tips and get inspired with others' collab part as time goes by. We all have learned a lot from all our past collabs because we're always talking to eachother, no one is "inactive", and our main objective when making collabs is to have fun and learn something new.
So yeah, I don't understand what do you mean by "serious" clan. I've seen clans go by that have the intention to be dead serious, creating alt accounts only for their clan, along with a personal twitter account or something like that and they still die a month after that. Improve and have fun with friends while still being a successful clan is not a "impossible" thing to accomplish. You just need a dedicated leader and active members that just wanna have fun and learn new things.