Riot thinks that every agent needs to be the best of the roster at something. Sage, for example, is viewed by them as their primary staller, no agent can stall as well as her. However, when KJ didn't have any radius on her turret and robot, she was as good as a cypher at holding places on the map without even being there, which is Cypher primary role. Therefore, they put the radius on the turret and robot to avoid her be as effective as Cypher in this situation.
I personally liked the change because it gives more variety to the game. I remember in the early LOL seasons, that some champions used to fulfil the same role as others. This created a problem because some of the champions were never used in pro play. After all, other champions would play the same role but were simply stronger. It seems to me that the current Riot approach to Valorant agent-wise is to avoid that happening again.