I'm very skeptical that helicopters can't safely operate at this temperature. It's likely a certification thing capped at the highest temperature they can actually test.
While there are plenty of certifications for aircraft maintenance and testing, this is legitimately a capacity issue. The air density issue is huge for aircraft. It caps maximum operating ceilings (as in the aircraft literally can't go any higher), it affects engine power (hence why things like intercoolers are an issue for performance engines), and it affects takeoff distance.
Ironically, it can increase the overall airspeed, since less dense air is easier to move through.
