I like your logic! Makes a ton of sense!
I also fully understand the legal 9.3 or .375 for Buffalo, but also struggle to believe that in a pinch a 358 loaded with 280gr swift a frames wouldn't be an adequate cartridge (I have zero buffalo experience to back this up).
Using a 300gr A-frame from a 375HH, my Cape Buffalo was unphased. Dying, but quite angry with plenty of energy left for mayhem. He charged and we shot the hell out of him. He turned and piled up, I shot him some more in a desire to end suffering. I was not impressed with the 375HH as a buffalo gun.
The 375HH is marginally okay on everything which no other caliber can claim, spanning the tiny-10 and the big-5.
The 404J is a much better choice. The 358 Norma is less-sufficient (and less legal) for Buffalo than even the 375HH.