The cartridge bearings in my front hub were feeling really rough, so I set out to replace them (never having done this before). I used a bearing puller to remove the old bearings. To my surprise they felt a lot smoother after removal, in fact one of them seemed as smooth as the new replacement bearings I’d bought. Is this normal, and what could account for this?

Deformation of the outer race as it is distorted or squeezed in the hub. A little squeezing is ok, is a press fit after all, distortion not so good. I guess maybe the pressure mean the balls run on a slightly different line or that they are running on the same line with less pressure.

What he said, they will be squeezed slightly in the hub.

Some hubs specify xxxx-C-2rs rather than xxxx-2rs which means the bearings are manufactured with slightly more clearance.