I recently joined Coral(iPoker) and have played a bit of 20NL. Only a small sample of ~7500 hands but current win rate is 15bb/100. I doubt the real number is much less lol.
That's just playing a straightforward Nitty-ish game too while I build some stats on people. However Nitty might be close to optimal on a site like this, I dunno. Yet.
Can't really answer your questions definitively, but for what it's worth - ipoker network changed a lot since they first introduced new rewards system and then the new software update so it's entirely possible that the games are far softer than they used to be.