I don’t disagree with you. A smaller end cap would help.I think it depends on how small, a 30 cal through a 375 is 0.075 smaller than bore. A 22 through a 30 cal is 0.080 smaller than bore.
I think the issues comes in with using the 375 for something like a 6mm at 0.13 smaller than bore. It can certainly be done.
One can to rule them all… .375”
Of course another can in 6.5mm for .22, .243, .264 would complement the .375
That said, I primarily got my .375 to run on my H&H and .358 Win