Let me make something clear.
Cartridges don't kill. Bullets do!
As a former CEO of a bullet company (Cast Performance Company in Riverton Wyoming) I am well qualified to speak on this subject.
So what is the point?
Any cartridge can be very effective if the bullet it's loaded with is up to the task Any cartridge is not going to be very impressive if the bullet it's loaded with is not suitable for the animal it hits.
The 300 Weatherby mag is excellent if you don't use bullets with jackets that are too thin for it's impact velocity.
Slower cartridges are easier to load for and usually a lot less expensive to load for, but if correct bullets are used, the 300 Mags are very good.