Well I'm messing with ya when I say ground squirrels, while enjoying doing so.
But I'm not when I say that as a general rule, the 338s will disable, anchor, and kill more proficiently, with the less than ideal shot profiles.
I know moose can be killed with a 243. Seen it done. That doesn't make the .243 Win the equivalent of a 300 Win Mag.
No more than the fact that moose have been killed with 300 Win Mags make them the equivalent of 338 Win Mags. They aren't the same, and some shots that become chancy with a 300WM, are almost certain death with the .338WM. Like it or not... Many hunters want a cartridge/bullet that will bring the moose down with something less than the ideal shot profile and bullet placement.
And the fact that moose are effectively killed with the 338s, doesn't make them the equivalent of 400gr bullets from .375s, 404s, 416s, 458s, and so forth. At the 338 level, I feel comfortable and confident. Can't say the same about the lesser calibers, even though I've killed moose with them. So I have multiple experiences with multiple cartridges - across the spectrum on moose. Take it or leave it.
I advise .338s or more caliber on our big moose, for those incurring the cost of that once in a lifetime hunt. Why risk it on a less capable cartridge? A guide isn't gonna let your moose run off with a wound from a cartridge he has little confidence in, no matter your view you're carrying the mother of all moose killer weapons. He'll take your money with a smile AND kill your moose. Do you want that hunt to end knowing you killed your moose, or that your guide killed it. Use a 338 on up, if for no other reason, your guide will understand it's the more worthy moose killer, and be a little less trigger happy.
Heck, I've killed lots of moose, and have a yearly opportunity to do so. I still prefer the 338s on up. Also killed them with 375s, but see less additional advantage to moving up that next step in bullet diameter.