I think it's easy to feel that way, but any time I've tried to measure this objectively on teams, pairing (I can't say I've ever measured mobbing) comes out ahead, even in terms of raw velocity. There's also knock on benefits down the road as IMO with pairing / mobbing there's less of a tendency to miss edge cases and so you're less likely to have bugs that need to be revisted, which is an enormous cost savings.