Agree with you fully on the 9.3 being extremely effective on game, as it will kill anything the .375 H&H will once inside the animal. Trajectory is a good deal more (half) pear shaped, but inside the typical ranges, it's more than flat enough. Only place we don't agree is on it being greatly different than the .35 Whelen, I see the two as American and German convergent evolution; heck they can both even be made from the same case and differ by only .008" and twist rate. A lot easier to say the .35 Whelen is an American 9.3x62 than to say the 9.3x62 is a German .375 H&H in my eyes.
This said, any of these will kill whatever you shoot with them. Then again so would a .30-06 99% of the time, we enjoy the 1% and write endlessly about the what ifs and obscure situations where more power matters. For me, it's not about power and ft-lbs, I don't choose .300s over .308s because they hit harder, Ichoose them because they get there much flatter with the bullet weights I prefer. .375 H&H vs 9.3x62 is more of the same, and given the .375's better bullet selection seals the deal for me. Effectiveness once in the animals I have zero doubt is identical, the .375 mags just allow it to happen from further away if necessary.
Last thought is recoil, I don't find an H&H to be at all objectionable, and a Model 70 in .375 H&H weighs what the 9.3s generally do as it uses a standard long action. So I'm not saving weight, couldn't tell the recoil difference between the two because neither is a handful, and in the end wonder why adopt another chambering that has lower limits than my already well practiced and used .375s... And I push that line of thinking on others!