I'm not sure who told you Groupee Community is for small communities, but that's just wrong. Groupee Community is the most scalable of the products and in fact one of the largest forums on the Internet (ArsTechnica) uses Groupee Community.
Also, unless you are currently hosting your forums on a computer you own, in a facility you own, you would lose no control by using one of Groupee's hosted solutions. It's no different than hosting your forums with a web hosting company from that perspective.
