Ever watched a monster truck? 10,000lbs, 1200hp, 66" tires, what kind of brakes?
more like 1400 to 1800 hp... most guys run 540 Merlins for reliability and cost. some will run 572's and a few 620 Merlins, and even fewer running big cid hemi's (last i saw Bearfoot [years ago] they ran a 598 hemi at 2000+ hp).
pinion brakes do work - they work extremely well for full braking ability. because of the small surface area but compounded by the huge leverage in gear ratio (monster truck example: ~6.x:1 axle ratio + 3:1 hubs = 18.x:1 advantage), pinion brakes are extremely touchy and are more of an ON or OFF thing. this also adds to their extreme heat production as well as exponentially short lifespan.
the point that was made is very true: pinion brakes are extremely traction sensitive - watch that monster truck again closely and you'll often see a front [or rear] tire either skidding or slowly rotating in the opposite direction.
also, pinion brakes on the street w/ lockers is an extremely wild and dangerous ride - there's no telling what direction you'll go when you slam on the brakes. even with an open diff, wet pavement can easily lead to disaster - not only can you lose braking ability, you can lose steering ability.
pinion brakes need to remain on dedicated off-road rigs and tractors.