You are correct, the demands of the carrier PCB are less stringent; but I believe this thread has amply demonstrated that this is not a zero-effort in all cases.
I agree that if it is possible to design a carrier where the antenna section of the module (be it P1 or Photon) can overhang that is optimal (at least electrically, if not mechanically) - but at the solution level it is still quite possible to screw up the RF environment by placing wires, metal work or other hardware in the area of the antenna.
Some validated reference designs and proven community projects will help a great deal.
I am curious what exactly it is about SoftAP mode that makes it more sensitive to problems with RF - I’d be interested in peoples opinions on that.
The AP is responsible for coordinating the packet transmissions of the client(s) - so it might be that if there is perhaps a less-than-fully-featured AP implementation in SoftAP mode, then it is easier for the wheels to fall off the coordination role.