Original poster is correct, character responsiveness, while alot better than OFP and ARMA 1 is still lacking and this has nothing to do with realism. In real life, no matter how much I'm carrying (in fact more makes it easier) I can hit the deck faster than this. I can get up, get down, sprint, dodge, or anything else more seemlessly than ARMA 2 allows me.
The game's objective of realism is no excuse for sub-human character responsiveness.