I agree with all your points, especially this last.

As a useful cartridge, the .45-70 is.

I am a real fan of the .45-70, but...

I believe it is a really stupid cartridge to chamber a double in unless the rifle is proofed for very heavy loads, because that is probably what lots are going to see anyhow whether proofed for such or not, just as you say, John. I bet the lion's share of buyers of .45-70 doubles wish they were .450's and plan in some fashion to make them such, or as close as they can till the barrels wobble.

I personally would not buy a SECOND-hand Baikal .45-70 unless I knew for certain sure that the gun had only been shot with pussywillow loads only.

Just my $.02.