I think the only issue would be that even a 1.75× multiplier for the SVK would cause it to just be a semi auto sniper with one tap headshots, not a dmr (a headshot already does between 85 to 90 damage on a full health target, which is absolutely fine imo). Its niche is a 2 shot, slow and steady fire rate dmr, and its relatively easy and predictable to use in my time using it, since it rewards careful shot placement and accuracy, and punishes spamming. I think you have a fantastic argument with that aside, specific headshot multiplier values for each dmr are probably needed based on their base damage, but i really dont think the SVK should be the new SR338 or whatever that semi auto sniper was called in bf4. The other dmrs really do need some love, the LMR especially.
I don't think that (certain DMRs being one-shot-kill) would create that big of an imbalance in the game or jeopardize the sniper class. Snipers have bigger scope magnifications (I didn't check on DMRs), and will predominantly be used by the recon class, and their headshot kills are "fatal," unrevivable—which DMRs or any other headshot don't achieve.
I can't think of any old-school FPS (albeit, most are placed in the WW2 era) in which you didn't have the classic Kar98K being a one-shot kill (not even HS). High risk & high skill = high reward. Even the M1 Garand had its role.
But let's face it, such skilled players are a minority. My guess is that somewhere along the line, most FPS games decided to strengthen automatic weapons so that the majority of the player base can feel competitive. Nowadays, I struggle to find a game in which automatic weapons (Carbines, ARs, LMGs) are not overpowering this class of weapon. I would even say that putting certain weapons on semi-auto mode gives you roughly the same outcome as having a DMR. The TTK of some of these weapons over distance is ridiculous and breaks the balance. I even got killed the other day by a guy with an SMG at 100-110m. That simply shouldn't be possible with their bullet caliber, recoil, etc.
