In CQB, the ranges are more or less airsoft ranges, so apart from being able to dodge BBs and not being able to shoot through most walls and doors, it works out great in CQB.
Ammo weight isn't a big deal, but it would definitely prevent people from carrying 24 mags lol
In the field it's more annoying to have realcaps, but it's not as bad as you might think. Otherwise nobody would have a GBBR lol
If you ran everyone on realcaps, most people would be really outclassed by high performance guns like tuned AEG's, GBBRs and PTWs. So although it's more realistic, what's not realistic is the fact a stock AEG can't hit the broad side of a barn on a good day.
Given that everyone has a high performance gun, the field can be leveled with realcaps with no complaints.
That being said, if you're looking for fairness, the better your gun is, the less ammo you should be allowed to carry.
I used to carry 18 lowcaps with my M4 aeg, 1224 rounds.
With the ptw I usually only carry 9 mags loaded to 60 each, that's 540 rounds. And I gotta say I refill them a lot less frequently, too.
So to summarize, the shittier your gun is, the more ammo you need to compensate for the lack of accuracy.
The more accurate your gun is, the easier it is to deal with running realcaps.