I can see that it is thicker on the belt face, its the other face that looks the same. The radius looks a little bigger, It should be as big as the WP flange allows. That radius has to support the belt face, all the flexing is acting on that radius and the side wall.
I always go by the rule that you make things as strong as possible within reason. Taking off less material saves time and you have less chips to get rid of. As my previous post states steel is a better material.

Bearing's
Roller bearings are out because of the RPM's involved. They heat up too much.

Stainless steel bearings are all stainless steel construction, using different grades of stainless for ***** and raceways. I do not think these are as good as the regular steel in this application.

The best steal bearings I can see are those that are used stock #6303Z or ZZ not RS or 2RS If two bearings can be used in a redesigned pulley that is better. Grease lubrication not oil, oil will need to be added too often as it will come out of the seals.

Ceramic Hybrids would be the other choice again using the Z type seal.

Different makers bearings are used because they are purchased by the idler manufacturer on a cost basis. It boils down, as most things, to $$$$

The bearing 6303 is a standard size (17mm ID x 47mm OD x 14mm wide) and variations of it exist, material, seals etc eg. SS6303ZZ, 6303Z, 6303RS, 63032RS etc.