The trick to good team comps is synergy. The comp you outline is a powerful teamfighting setup, so you'd want to use it to force fights on objectives to win. The big glaring weakness it has though, is a lack of poke or waveclear. That doesn't mean your comp is bad, it just means that you need to be aware of such a thing. You could mitigate it by changing champs around, but you might be sacrificing AoE ult power to do it.
There's a lot of different strategies that work in the game. Your comp is best suited to stomp around as 5 and force fights whenever your ults are up. Other comps might be best suited to trying to stall while whittling the enemy team down with poke (your comp is well suited to counter this strategy though, since you can pretty much tower dive at will). Others might be built around a tough defensive team with a split pusher (your team would be weak to this since they'll have someone like Janna or Alistar to reset the fight, and losing anyone from your group weakens your wombo combo significantly).
There are more than those too, but I hope you get the idea.