If it were like the M14 but worse in every way and heavier except don't worry, guys, it has medic darts...it would be trash in the eyes of both perks just like the others are suggesting.
But. If it were something like the BD Hunting Rifle from KF1 with a KF1-style dart launcher that had no guidance system, it might actually end up being something worth using. The comparative difficulty of unguided darts and force reduction of a bolt-action platform could lead to a weapon with high enough damage to still be worth something to Field Medic without being either useless or overpowered for Sharpshooter because it's a completely different piece of kit that sits somewhere in-between the Railgun and the M14.
My logic: Bolt-action means both a slow rate of fire and, more likely than not, small magazines, which means it has to be significantly stronger to compensate. Therefore it could be balanced to deal enough damage that it could actually be useful for Field Medic without being anything too crazy for Sharpshooter due to low rate of fire.
Perhaps not sniping scrakes solo as Field Medic in a 6-player HoE match, but damaging enough to be helpful for scrakes and to solo that scrake if you absolutely had to. It would probably be strong enough to pick off everything else (sans flesh pounds, obviously) with one or two shots, which would be great.
An unguided dart launcher would make it harder to use in comparison to the other medic weapons, which would therefore make it get nerfed less simply for being a medic weapon. Also, as stupid and impractical as it actually is, an unguided dart launcher also makes thematic sense for a "sharpshooter's medic weapon" such as this. At least they would be hitscan and you have a scope.
Being exceptionally heavy is also an excuse to make the gun itself better because it can't be supplemented with an entire extra arsenal. At least it would have plenty of ammo (say, 160 rounds in 10 round mags).
Tier 3 sounds like a good place to settle this into. 9 weight blocks also sounds perfect. On the Field Medic side that could pair, unupgraded, with an unupgraded medic shotgun or fully upgraded with a medic SMG upgraded once. On the Sharpshooter side that could pair, fully upgraded, with an upgraded .500 magnum or unupgraded 1894 lever action rifle.