Well, arguably Susan, Barbara and Ian counted as three. And Unit era you had all of UNIT as well as Liz/Jo/Sarah Jane. Also a few with Nyssa/Tegan/Turlough before Nyssa left. And possibly Jack, Rose and Mickey (granted there were very few with all of them in it).

I think it only unbalances the new format if they keep going with the "ooh she's so in love with him/ooh she isn't in love with him at all" dynamic and left it for a while.