I am not a fan of that concept. I prefer the topic discussed to the end, where everyone agrees.
Why should I operate according to MEL for gear U/S, just because I delay retraction?
Rhetorical question:
In the example of NOR8F, I have to delay flap retraction to 4000 feet as well, as I can't afford to accelerate if I want to comply with the altitude restriction at 4.8 NM KBO VOR. Engine failure procedure will have me retracting them at 1900 feet (1500 feet AGL). Should I in this case check the MEL for restrictions for flying with flaps U/S?
Obviously not. Why should it be different for the landing gear?
The AFM defines what a normal takeoff might be, not the pilot on the day.
Wrong, the pilot operating the aircraft needs to be flexible, and make sure to comply with the challenges of each individual departure. For that, the performance manual is a tool to support the pilot in making good decisions.