First, 'WWII airplanes' is a pretty broad category. Each craft has different characteristics.
Second, once you learn the best altitude and speed of a specific plane then you'll find its sweet spot.
Third, you won't be in that sweet spot the moment you level off. You may have to do a shallow dive to get there quicker.
Fourth, yes, you may want to consider scaling your stick in settings if it is spiking. All the system sees then is a ham fist.
There may be more to this. I'm sure others can fill in.
Almost forgot - not every plane is suitable for every player (at least not in the beginning). But, practicing with the ones that give you the hardest times can eventually be rewarding.