The controllers would work great in gameplay like rainbow 6 siege. The maps dont

If you had a map design like R6S controllers would be very useful tools. But all maps are highly open. Every time you build another map, it gets more entrances to buildings, and more vertical floors to buildings, and that dilutes effective toolkit of controllers.

The maps are designed to be opposite in all ways to controller characters. Add onto that there are many other characters that have controller like functions in recon and support class but their tools work even better in the open and the class controller is redundant.