It's not just the difficulty of micromanaging multiple classes, but the effectiveness towards an individual's goals. Some people pve, some try to do heroic and raiding pve, some mostly BG pvp, and others really enjoy arena. Shaman can work well in all of these. While other compositions may potentially be more effective in any one or two of these categories, a shaman group will give the most variety of end game capabilities. So it really comes down to what your goals are.

Personally, my favorite group to run so far is priest with 4 lock. I expect I can do all normal 5 mans and own in BG's. I don't know if I will do very well in heroics with void tanks and I doubt I will be effective in arena.

Your group has more variety and could probably perform better than shaman groups in many pve encounters. However, don't expect your balanced group to excel in arena.