That makes sense logically, but if you think about it, GPS is still best for efficiency. If you're heading into a certain direction and GPS is not fighting the wind for you and keeping the AC direction aligned, then you will have to fight the wind manually which won't be as efficient as the computer doing it for you. And you'll almost certainly end up taking a longer path.
Also, there is more to ATTI than the manual leads one to believe. It's not just about lack of GPS. ATTI is like injecting nitro to a gas engine. It makes the motors race. It's similar to "sport mode" in the P4. But at full throttle, it causes the battery to come down in charge quickly and is inefficient. And at full throttle, it's also dangerous on the latter end of the flight because voltage lag is more pronounced which can cause auto land or worse.