1.The belt of a cartridge does not make it handle higher pressures. It is strictly for headspacing. (The RUM cartridges, Lazzeronis, Lapua and WSM are not belted and operate at the highest allowable SAAMI pressures)
2.The .400H&H offers no advantages over the.416 Ruger and the .416 Rem.
3.Making an argument for the difference in SD between a .416 and a .401 is ludicrous.
There are .410 gr and 450gr Woodleighs available for the .404 and for the .416 with higher SD(.361-371).
4.There is no need for a .400H&H, except to sell bespoke rifles and proprietary ammo,as it offers no real advantages.
I respect the right of any gun owner to own whatever makes them happy without the need to denigrate well established classics or superior cartridge designs.