Nah. I'd put about ten mags through my G21 and inspect the bore. It usually just had some lube residue that would come clean with a mop. It was certainly cleaner than a regular rifled barrel.
As mentioned, they don't all lead the same amount or at the same rate.
There's also the issue that because of the smoother barrel profile, it can be more difficult to detect leading. Had a guy on another forum swear up and down that he had a G17 with a shot out barrel that appeared to be a smoothbore. Turned out the barrel was in great condition, it was just leaded so badly that he couldn't see the rifling.
It's a good thing he cleaned it before he tried shooting it.
For what it's worth, it's likely that the lower velocity of the .45ACP probably makes the G21 less likely to lead. Still the problem is that there's no way to say for certain how much of a given lead bullet load will be safe in a given pistol.