It helps, but honestly even the figures I cited are probably way too low as it is; thicker air by a factor of 2-3x might almost bring it into the realm of possibility, but no more.
Consider that the double axe has at most 2 sq ft of airfoil with a radius of maybe 4-5 ft, while human-powered helicopters need (at 16-18 Str and probably 16+ Con) multiple 20' radius rotors operating in ground effect to manage a minute of hovering at max; total area is something over 300 sq ft. (That is, they're gaining a substantial boost by never going more than 2 ft off the ground.)
Dragons arguably fly partly by innate low-key magic (much like the magic that holds undead or constructs together); also, they're designed to fly, and have big enough wings to manage a small margin (i.e., enough to perform wing buffets).not being able to do anything while flying defeats the purpose of flight. poor maneuverability requires forward momentum, unless you spend yet another feat on hover. making the feat weaker for the purpose of realism is a bad way to go, especially in a world where dragons fly, and can still make wing attacks in flight.
Humans (or elves, or dwarves, or other substantially similar races) are not built for flight; our power-to-weight ratio is horribly low in general. However, if I wanted to be mean I'd say make the feat give nothing but hovering; actually moving anywhere, or getting more than 15' off the ground, requires another feat and still higher ability score prerequisites.
Ah, jokes are often hard to detect with certainty. Sorry.
This is true enough as far as it goes, but sacrificing all manner of plausibility in order to correct metagame balance concerns is not, in my opinion, a good way to deal with things. There are some existing ways to (partially) solve this, or you can design a martial class that is not fully mundane in order to get around it (Ranger animal companion, Paladin special mount, etc), but there is no way you are going to get decent flight without either technology (usually involving fixed wings or compact engines or both), magic, or overtly superhuman beings (in which case the magic is in their muscles/wings/what have you).