I believe it's more the fact that rimmed cartridges operate at lower "Handi friendly" pressures than rimless, but I've not had any problems getting very acceptable to excellent accuracy in either of them. A lot of Handi owners will say they like rimmed rounds better, but a lot of the reason for that is because of the lower pressures, they weren't a problem due to sticking brass, which is a moot point with an extractor, and also for an ejector with a good chamber and mild to moderate loads, too hot loads may still be a problem tho.
Tim