yeah 4,000 per day of play is way too much especially for a front guy. Maybe a dedicated backman who's job is only to lay down paint for his team, but this scenario is unlikely at a regular rec field. Say a case maybe and if there a bunch of people on each team. To me 500 is normally plenty, though I can do less if the piggy bank requires it. 1,000 and I feel like I can pretty much hose away with a mech and not worry to much.
your point still stands that day to day playing costs are cheaper in airsoft and thus do allow you to shoot way more rounds. But it isn't really necessary to have to shoot the same in paintball.