It doesn't seem to be entirely isolated. Apparently going back to the old app switcher requires you to freeze or uninstall the system launcher, no matter what launcher you're using.
Gotcha, ok. I started using Android ~1.5 I believe, so things have changed radically since the beginning. I recall this being the case in ~2.2 perhaps.
I used Android from 2.0 to 4.4, and the phones I had performed notably better with third party launchers, suggesting the original launcher process wasn't still using system resources.