I will say that I think leaving behind our party after act one would have resulted in a worse game experience. The companions are essentially the backbone of the game. Taking them away would result in a far less interesting experience, if you ask me. Plus from a mechanical standpoint, you'd end up with people leaving behind certain characters and just never experiencing them because there's no room for them in a party. I like Wyll, but I know that if we would be limited to only three other party members, I'd never take him past act one because I'd never be able to justify having him in my party over anyone else. The same probably would go with Gale, since I like to play spellcasters so having him would be redundant, especially since Shadowheart would be a definite keeper in the party for healing. I'd probably HAVE to take Astarion because having no rogue at all for the game would be a rough prospect.
I also don't think it would have improved reactivity within the group because they'd still need to write more or less the same amount of dialogue for everyone.
