The map in FH2 is much smaller, if planes don't maneuver as quick or take-off as fast, they waste too much space and easily fell prey to expert AA gunners. Moreover, I feel that the draw distance in BF2 engine is severely lacking to have a proper FH1 style realism.
FH1 has better combat system, because it has better draw distance, better map size, and more geared towards vehicular combat, rather than "enhanced FPS".