We should probably observe where the big pulleys (13t) show up.

1. They are on Alivio and lower classes like Altus, Acera and maybe 2300 RDs. So the standard higher end RDs still sport 11t.

2. Lower end pulleys use BUSHINGS. Not bearings. Even higher end are still using bushings for the most part. But we're talking simple, cheap, bushings. Maybe after-market has bearings. Regardless, wear was never a problem here on the bushings. The problem was tooth wear in the face of cheap plastic. The higher end RDs can sport expensive polymer pulleys. But on the lower-end, with thinner teeth to accommodate 8/9 speeds, this is a cost factor. Solution: More cheap plastic to reduce individual wear so there are 18% more teeth and therefore 18% longer wear, which is lost because now the teeth were thinner. But we can now get the same wear life with thinner teeth using bigger pulleys, which are still cost effective because of cheap plastic and the see-thru interior which reduces the amount needed to cast these.

3. Bigger pulleys effectively pick up more chain because the diameter of the pulley increases the effective radius of the RD arm. It's the same effect as a longer cage. In fact, the amount of chain pickup is pretty much dependent on the cage length of the main lower arm, and partly on the upper body B-rotation to some degree. The pulleys don't have much to do with this except to increase slightly the effect lower cage length and the effective upper body extension. So no real effective difference. And note, with the shadow Deore/XT/XTR RDs with small pulleys, and long arms, they have slightly greater capacity than the Altus, Alivios, etc. Because they have longer effective cage length despite smaller pulleys.

4. Less chain angle, more distribution of load on more cogs, yes. But the wear isn't less on the cassette or the chain per se. That was never the issue. If we're talking less friction in the drive train, I don't think that was important either because if so, why not have them on the higher end? The chain is under massive tension when riding on the top portion of the chain. The friction going through the pulleys is second or third order if at best and not significantly different between 11t and 13th. The bigger pulleys require more wrap around the cassette - more friction. But are gentler on the radius when the chain bends around. Less friction. It's a wash that's 4th order if any.

Personally, I like the big pulleys. It's looks beefy psychologically. It makes feel like the derailleur is more expensive than the $15 I paid, and the big plastic pulleys with the spoke wheels do make it more aerodynamic until mud clogs them up, but then I feel like I know when I've cleaned them when I hose them down and I see daylight.