Well there's no doubt a proper sized 450 3 1/4 action is trimmer and a bit lighter than a 470. I don't think that you could tell the difference in recoil though. They are all so close in power as to not matter which you take hunting. If you think you are going to find 470 ammunition in Zambia or Tanzania you are really in the dark. That's why it doesn't matter what cartridge you take.

I think some people want something different than the herd so they choose a less popular caliber. Also a lot of people buying Doubles now don't really have a clue as to any of the calibers or makers so they buy what appears to be popular.

I would be happy with any of the 45-47 calibers if it was the right rifle.

Bullet design has nothing to do with it. The Kynoch style has been with us for 100 years and has worked grand. Some people leap on any new design because they just have to screw with everything or they aren't happy.