Canton = make group troops

Why not a building where you can make an army of combination of 2 troops :
Example = 1 Giant & 5 barbarian army
All stats will be same but training time will be 30% more [ total ] , cost will be 25% more [ total ] . Others will be the same .
Unlocked at TH4 and has 13 levels. It has certain predefined combinations only.
So what is the gain ??
Considering the example , the target of all the troops in that mini army will be the same.
IE 1 giant and 5 barbarians will attack nearest defense and never have separate targets
The combinations shouldn't be too OP when used like [ LavaH & 6balloons that target AD first ]

Thnx