i can't say i've done any kind of formation flying... other than being towed aloft in a saiplane 

but i think that the sim IS harder on some aspects, many of which apply also to flying helicopters...

first, you have NO depth perception... it would make a world of difference if you could perceive yourself getting closer or farther away from your lead plane

also, the joystick will never replicate an actual control stick / yoke, no matter how good... but it does help to have a high precision joystick... i know my flying improved sensibly when i traded over the old MS FFB stick for the X52

plus, your vision is tunneled by the small area of the monitor... a triple head setup helps a lot, but you'll never achieve TOTAL immersion... even completely surrounding yourself with monitors... and that might be bad for your eyesight 

so the sim has it's limitations... but at least you can harass the air traffic without fear of being arrested later 

Cheers