Just my thoughts:
I believe MOT_THST_EXPO should still be close to a standard value based on your prop size, at least as a starting point. The thrust curve mostly changes because of the prop rather than how well the motor and ESC track the demands from the flight controller. Most modern ESCs will be quite good in this regard, see BLHELI and AM32. Unless your ESC tries to linearise the thrust somehow, but then there would be some setting in the ESC for that to suit different applications, or the ESC would come in a set tied to the motor and prop.
A thrust stand will give you good results if you are OK with using the spreadsheet correctly, but keep in mind: that is static thrust. So in reality you probably want some value that’s an average of the static thrust expo value and some expo value that might be in play during forward flight and other maneuvers.
Generally you can test your MOT_THST_EXPO by doing some ascents and descents and looking for instability, provided tuning is quite good - for a multirotor of course.
- set too high you can see instability at low throttle
- set too low you can see instability at high throttle
If you make a significant change to MOT_THST_EXPO then you also have to retest and set MOT_SPIN_ARM and MOT_SPIN_MIN
Leonard Hall is the king of this sort of stuff and will have much more scientifically-backed information than whatever I say.
Check this: