I don't doubt the rifle in the hands of a trained and experienced soldier is deadly but there seems to be a number of complaints about the quality of training from conscripts even having the best rifle in the world would not make me a sniperStuff and nonsense. You've posted several links to western articles talking about the Mosin use in general terms. None have specifically addressed its use. This is just propaganda. Not lies exactly, just very misleading. If you look at photos, it's got optics every time. And if you look at photos of LDNR reservists from the Mariupol' assault or from early in the war where they didn't have body armor and were easily distinguishable by their SSh-68 helmets and side pouches, it's always the same 1-2 Mosins at most in a photo, each time with optics, surrounded by other troops with AKs and PKMs. There is one photo of 4 of them (though these 4 had flak jackets), but again all optics, and the photo was labeled as an LDNR sniper section. There is 0 evidence of the Mosin being issued as a primary infantry rifle. All of the evidence and all info from the rebel side points to them being used as sniper rifles. And while we're at it, there is at least one NATO member that at least recently used the Mosin as a sniper rifle.
Russian Conscripts Given Guns From 1800s To Fight In Ukraine: Report (ibtimes.com)
Conscripts Sent to Fight by Pro-Russia Donbas Get Little Training, Old Rifles, Poor Supplies - Sources (usnews.com)
Certainly LDNR forces in this article were known to have been seen according to this article with them last year
The Famed Mosin Rifle Haunts the Russian Army | The National Interest