your math is so flawed that a third grader would pick it up instantly. Looking at 190 grain bullets in the Hornaday manual, I see a max load in the .300 Ultra mag as about 92 grains of powder and the WBY mag with the same bullet is about 75 grains. Both are over bore, but one is ridiculous. All that for 100fps!
Now lets look at the cases. The WBY brand cases a known to be made by Norma, and that's top quality in anybody's book. Primer pockets are machined from the factory. Wby. doesn't seem to shy away from bullets as well. They use almost nothing but the very best out there. Now compare that Remington case with the Weatherby.
By the way the .300 WBY mag is often regarded as one of the best 1000 yard cartridges made. Never heard that about the Ultra Mag.
gary