When you are new its a voyage of discovery, but without new developments there is nothing new to learn/master.
When is the last time you spent a tour (or even a day or two) in a Hurri-1 or P-39...or any airplane other than your favorite? There are many, many things (air and ground) to choose from to learn/master. Sure, you'll suck at them in the beginning...but doesn't everyone at first? If you care that much about your rank and score, then you are missing the whole point [IMHO] of this game.
I was bored flying cannon-laden planes and killing people with a .5 second burst. I've flown the Hurri-1 for a while now, and have had a great time because it forced me to fly better, more controlled and be more patient to set up the shot and keep the guns on target long enough for the kill.