Just Thought I would add my opinion to this question.
I build lots of accurate cartridges on the Mark 5 action. Lots of then are wildcats but lots are in standard Weatherby cartridges. With all the emphasis on big bullets and high velocities the Weatherby cartridges hold lots of powder and run at very high pressure (Good for velocity).
The case design is built around velocity, but accuracy Is not hard to achieve if the smith knows what/how to put one together right and head space it very close.
I personally see no advantage in the radius shouldered cases but again, they can be very accurate.
I feel the main reason that more mark 5 actions are not used is available actions and smiths that want to work on them. Remington style actions/clones are easier to work on and respond well to
any kind of accurizing and are very common so this is the style of custom or factory action that is most common. The reason the cartridge are not as popular is the radius shoulders and the belt.
Belts are also not a problem if they are set up correctly. and if a person does not like belts the simple way to change this is after fire forming. neck sizing ONLY will change the belted case to a shoulder head spaced case.
Also the Weatherby cases themselves are quite expensive and don't last long at the pressures they are normally ran.
So most people will build a match rifle that brass is easy to find, and components are readily available. also very simple and straight forward to load for.
The cartridges and the actions are second to none if every thing is right and can/do compete. they are just not as popular as other choices.
Also most matches do not require such huge amounts of powder and velocity so the big cases and actions are not necessary.
Just my opinion as to why more Weatherby cartridges and actions are not used.
J E CUSTOM