Well that MW2 thing looked pretty hectic. I don't think the point is whether you can count the precise amount of players on the map at one time on your screen. It's a matter of how many are in the same skirmish as you. In the Rust map, you see the guy dying every 5 seconds, so you feel the added players on the smaller map. The gimmicky part of MAG I suppose is the advertising. MAG doesn't feel any more hectic(I'm assuming, haven't played it) than Battlefield BC 2, which doesn't feel any more hectic than a normal mode on MW2, because the size of the maps are all pretty equally proportionate to the amount of maximum players.
Kylie basically says it right above me. It doesn't feel different. The 256 players exist, but they exist too far away to matter to your on screen action. I couldn't imagine there being anything as confined and as hectic as that MW2 video, because that video obviously has 2x too many players in it, making the conflict feel larger than even MAG, at least on screen.








