Roller bearings can probably take more load radial. I've never handled one in my life. I knew any bearing is magnitudes better than no using bearing, so after that I stuck with what I knew. The prices are similar so I figured that there's some sort of tradeoff that I didn't really know about first hand. So in the end I stuck with what I was familiar with.

Research indicated that roller bearings take more radial load and less axial load, and ball bearings have less friction. I have some experience with pneumatics during my days building potato guns, and I know how to calculate torque with my rotor size, I judged that the radial loads involved would never a few dozen pounds, and ball bearings can take that easily. Roller bearings are rated to thousands of pounds.

The tubing is centered naturally, the casing itself has as slight taper so the tube centers itself. The bearings are tapered. No need to make the rotor assembly any thicker.