Take a look at the team comp. It is full of cc and is perfect for teamfighting, I will now explain why.

Firstly, there is a mixture of damage, being both AD and AP. AP is provided by Malphite, Sejuani and Janna, with AD being provided by Ashe and Yasuo (the main damage dealers). Malphite and Sejuani may not be building full AP, and may not be conventional AP champions yet they both scale well with it and will deal a lot of damage- especially Sejuani's E which she maxes first. Janna wont be dealing much damage, yet will be doing a fair amount of healing to both the squishy and tanky members of the team with her ultimate.

Secondly, we have the combo and engage of the teamfight. Let me go through what will happen for engage and in the teamfight if all goes well:
Malphite R engage
Yasuo R damage
Janna Q more cc
Ashe R and W damage and cc
Sejuani Q and W damage and cc
After a short while with this plan of enage and teamfight all members of the enemy team should be dead. Even if not all goes to plan, the comp is good enough to win a differing teamfight unless very far behind or the enemies outplay very hard.

Finally, the overall in game damage is very high and all lanes should be able to come out even or ahead unless counter picked. This comp can also fit into a 1-3-1 style with Malphite sitting bot with TP and Yasuo sitting top and pushing so the team can get baron control. This can ultimately result in a won game.