In all the training I've done a steep learning curve means to learn a lot in a little bit of time. Flying twice a day for a week for instance is better and gives you a steeper curve than flying twice a week for five weeks. But, WRT AH, I think the curve that best describes AH would be similar to a Bell curve.
You start out slow (a shallow curve)...figuring out all the buttons, stick mapping, views, landing, basic gunnery, etc. Once you have the basics down you rapidly improve (a steep curve) as you learn tactics and and the planes and also learn to fight "smart".
After a while the curve flattens again as you aquire more difficult advanced tactics, take on more challenging rides, are more willing to engage without an advantage, etc.
Then the inevitable occurs...you're on the backside of the curve and you turn to the dark side. This is a very steep downward slope. Work, food and family become just short breaks in your AH life but you realize you'll never get any better than you are right now. You fork over $500 for a new control setup thinking that'll make you better. Failing that you decide that the "/" and keyboard are more important than throttle and stick and spend more time complaining on 200 than actually fighting. You decide that every plane except the one you're flying is "uber" or for Noobs and Dweebs. You decide that any tactic you're not using is "dweebish". Absolutely everyone else in the MA HO's and Picks and are score ho's but you never, ever do that and you absolutely never look at your score. You're convinced that planes like the Spit 16 actually do fly themselves. You constantly challenge people to the DA so you can compare sizes.
Just my opinion of course
