Please don't make this change. I have another suggestion, although it's based on speculation. Some people in earlier posts have suggested that this change is to discourage archetypes or to encourage support archetypes. My suggestion is to implement a incentive policy for diverse teams. Like, you get a bonus for a TF/SF in merits if you have no duplicate ATs. This idea was partially inspired by the Kheldian inherent powers.
Homecoming has been running for over 3 years now, and the defense mechanic has been in place since the early days of City of Villains. Changing it now would be a mistake, even if the real-world effects aren't dramatic. Many of us players want the game to function as it was on live. We enjoy and appreciate all the new things too, but don't like changes to the basic functions. In short, add to the game, don't subtract.