Vlad - in this case, you are “not catching on.” You’re putting the cart before the horse. The idea was to be able to use bigger diameter cartridges in very fine gun designs, perfected befrore the desire to use a bigger cartridge, without having to make huge revisions in design and tooling to accommodate them. This was especially true before CNC machinery made design changes somewhat easier to do. Lots of the original rebated rim cartridges were big game cartridges, and were not expected, and did not, sell as well as smaller cartridges for game up to the size of, say, Elk. To change the dimensions of the action of a rifle would cost more than any profit made on selling them in the bigger calibers. Of course, in many instances, they ended up changing the actions anyway, like with the Mauser short action, the normal action we know generally as the “98” with its bolt face for 8mm Mauser, and the Magnum Mauser actions.
Today, many of the rebated rim cartridges were designed so that people could convert their AR15 shooting platforms to bigger calibers.
By and large, in each case, the idea was to adapt an existing firearm to a caliber for which it was not originally designed, with an absolute minimum of effort (basically, screwing in a new barrel and perhaps some magazine box and feed guide work.
I am not a gunsmith or very technically minded (gee - that will be a surprise to the members of this Forum : ) : ) ), so this answer is probably oversimplified, but I think it is basically correct.
If you are designing a gun from scratch, then I, for one, can see no purpose at all to the rebated rim, which of itself must be carefully designed to prevent head collapse upon firing.