I think that's defintely not right. We always put the leagues first; even when it's just a small league taking up a few of our lanes, everything's adjusted for them. The radio and jukebox go off, they get a 'buffer' lane, etc. (Although we are allowed to put people who bowl in other leagues up next to a league, if it's the only lane we have, provided that they practice lane courtesy and all.)
I'm also not sure why they didn't give you a reasonable number of lanes. In a few of our leagues, we have multiple lanes that are assigned to entire Vacancy teams. The Sports Shot requires a special oil pattern, so we keep two lanes on hold in case we need them.
We could easily compress our leagues to get some more business, but we don't. It'd just make a total mess of things, and upset all our regular customers.
On the other hand, I've always thought an unsanctioned cosmic league would be a lot of fun. But I don't think it'd be as much fun if you weren't expecting it to happen!