That's pure baloney. The diameter of the pinion depends on just three things: 1. Ring gear diameter 2. Gear ratio 3. Where the pinion is with respect to the ring gear.
If you want an 8 3/4 with a larger diameter pinion, get a 2.76 gearset.
If you want more teeth to engage, get a Ford 9", the pinion is lower on the ring gear.
Otherwise, you're stuck with how Mopar engineers designed it. They put the pinion higher to increase efficiency. They decided on 8 3/4 as a good diameter to provide adequate strength, not being soothsayers (who could see people hooking 600lb-ft engines to the front and with 3500 lb on two 12" wide tires on the back.)
The REASON the gear teeth break is the pinion and ring gear are pushing away from each other. The farther apart they go, the more the moment on the gear tooth root increases. Voila! Teeth break.
There's no magic involved. Ford's 9" has a slightly larger ring gear but the major advantage is the pinion is supported on both ends. This is also the 9"s biggest disadvantage as well, there's no room for a decent limited slip because it'd run into the pinion support.
