Why superior? The krag had the shortest service life of any us rifle short of perhaps the Lee Navy. All are built to be as cheap, simple, easy and rugged as possible.....every single one of them, One example got it's start by cutting up stuff that was even older, the trapdoor system defines cheap.
Everyone of them from that time frame will be par for the course on what they are designed to do, put a hole in something at X distance, and do it in a reliable manner.
I contend that the MN is really no different from any other service rifle at the time. Make no mistake I am not fan of russia not in czarist form, communist form, or the current form. However we are talking about an item. Looking at the item itself. Now looking at the worn out examples most of us have laid our fingers on....sure most still work, but are very far from mint....even far from in good shape. Way back when they got pulled from russian service ole Olga used a 40w bulb that the shade was once her husbands head to make sure the thing still was a gun that went bang, then it got stuck in a warehouse for a few decades to be sold off to americans. The examples most of us see fit into this group. People at one time said the exact same thing about Japanese rifles, French rifles are a dropped once, and Italy only made garbage, all this has changed. Gun Jesus on youtube made everyone look at french rifles differently, he likely had a hand in italy as well. Do you think that the russians are really that bad.
I will leave it with this.
I always thought carcano was kinda clunky, a bit junky, wobbly bolts and such.....but for some reason I don't know why I liked the little things. Perhaps because they are so cheap. Then I came across one that had spent its life in a museum dressed up like a LHO rifle.....I bought it for likely more then I should have. And it changed my view on the rifle. It is tight, crisp, and feels like no other carcano I have ever had. Having a good one changed my mind.
Then I bought a minty US mosin, I think I put pics up. That one (still not shot it yet) has a bolt that feels like no other mosin bolt I have ever touched, other people agree, this one feels so different, guess because it is american........or could it be because it is not rode hard and put away wet.
I didn't say or mean ALL on your list were superior, I said most. In fact, I'd be pressed to pick a worse rifle than the Carano, at least the shortened ones done is a shoddy manner from surplus ww1 examples.
My 91/30 is very very mint. Outside the finish on the stock starting to show its age, all the metal is about as pristine as I've ever seen on a MN. It took me hours to clean the preserving greece off it when I bought it. The bore is perfect, the scope is perfect, the stock cuts for the scope mount are perfect and age seasoned to match the rest if the stock, near as I can tell, everything about it is 100% correct, real, orginal, early import before knockoff 91/30s snipers started showing up in the early 2000s.
That said, its safe to say its the cream of the crop of all the surplus...doesn't get any better. Its a good shooter, with careful handloads, but the best it does is 2-2.5 MOA. Plenty plenty good enough to remove the heads off careless Nazis at 200 meters in Stalingrad, even good enough to hunt deer in PA, but it isn't, and can never be, anything close to what I'd call a tack driver.
On the other hand, I came across a 1942 matching numbers Mauser 98k that someone had drilled scopemounts into back before it was worth anything. It too has a perfect bore, and it was well cared for by whoever had it before myself. Since the damage was done, and its collector value null because of said drilled scope mounts...I went the rest of the way with it and put on a decent stock and trigger, and its a tack driver. Sub MOA all day long, any temperature, dang near any load save to worst surplus garbage.
Its a better rifle in every way...even before my mods were done to it. It was a great shooter before I put a dime into it.
The wood and metal finish, while not compatable to modern custom rifles or most commercial ones, on the original stock, where more than a few steps above the MN...and the action far smoother.
The Germans clearly put more time, better talent and material into the Mauser than the Russians did for the MN. Saying that doesn't mean the MN is crap, but it does mean its not on the same tier as a Mauser...or Springfield..or maybe even SMLE.
It was the tool best suited for Russian needs...nothing more.