Recently I had a test flight agaisnt the wind. At first I was flying in GPS mode and my mavic seem beaten by the wind and drifted away even with 100% throttle. Of course I took back the control after I switched to Sport mode manually.

I have 2 questions:
1. If someone (say a beginner) press the RTH in GPS mode in the windy situation like this, will mavic auto gain power (like switch to Sport mode temporary)  to agaisnt the strong wind to fly back?
2. Can I suggest to add a warning message if the 100% throttle was used but the drone still going in opposite direction?

No! It doesnt!
I saw another thread here where some one wanted autonomous return in windy conditions.... ffs....
In Sport mode your flight avoidance systems are disabled. The mode is intended for experienced pilots get more out of the aircraft, nothing more..
We get enough, I lost my Mavic in high winds type threads now....Can you imagine if DJI implemented this type of flight mode..... How about "My Mavic started coming back in RTH. Switched into sport mode and smacked into the side of a house that was between me and it... it must be DJI's fault..."
Fly within your ability I say, when push comes to shove, hope that you've learn't enough to stop the thumbs shaking, and get it home. Or PLAN B, land safely and go get it.

No, RTH will not increase power in windy conditions.  You're best bet in those circumstances is to avoid  (or cancel) RTH , switch to Sport Mode and return manually.  Depending on wind direction, you may have to do some crabbing.  Remember to watch the battery usage.  As was mentioned earlier, Collision Avoidance is off in Sport Mode, so be vigilant!    If you're  flying in a relatively unobstructed area, you should try lowering altitude to possibly lower winds.


2.  There is already a high wind warning.. No need for a Very High Wind warning.

Honestly it is the responsibility of drone user to ensure that it is not too windy to fly. Check the weather forecast, local condition etc. Drones are not toys and they should know everything and anything about the drone capabilities and limitations.