I'm on board with the majority thus far...
CAN that 257 Roy work on a moose? Sure.
Would I personally choose to use it? Nope. Not even on a dare. It could work, but if I'm putting my time off, my money, and my effort on the line, I want something with a little more margin built into it in my hands when my moment comes.
One of the reasons I tend to select more substantial cartridges than needed for deer is that I am usually pretty confident that I will get an opportunity at whatever it is I'm hunting. At some point. I may well only get one chance, and it may not be an ideal shot angle or distance or whatever. So I want something that's up to the task when things aren't perfect.
Now, don't take that to mean "I'll take Texas Heart Shots at 700 yards because I have a [cartridge designation here]."
What that means is when I see my buck I want to shoot and he's at 200 yards quartering at me, I want a round that I feel very confident will bust through the shoulder and get to the lungs and out the far side.
And what gives me comfort of mind that such will happen can and will differ from what will make others feel comfortable.
For a moose hunt, I'd have been quite pleased with a 35 Whelen in my hands. I think that's an excellent choice, although I've never hunted moose. Mooses? Meese?
Anyway....I also agree better choices for that application exist.