The Kraber, relatively speaking is pretty awful for what it is.
Scope in time is insanely high (0.58s) with no way of reducing it. So this weapon is enormously difficult to use aggressively.
ROF makes the damage output pretty useless on its own. Sure you just hit someone for 125 or even ~188. They take cover during the ~0.83s you have between shots (not including if you need to unscope and rotate to get an angle again and take that 0.58s to scope in again) go use a phoenix kit or health drone + shield battery and they're ready to fight again and odds are you won't get another hit in because they're aware of you. Add on to it that the Kraber has the slowest bullet velocity among all the sniper rifles means it also the hardest to get a hit in at range.
So Kraber is worse when used in close range aggression, worse in long range picking, and worse in mid range engagements than literally all 3 of the other sniper rifles. The few situations that I think kraber does well basically every Assault Rifle, the DMR, G7 Scout, Wingman and Peacekeeper would be significantly better options especially since you have ammo for them.
Side note, Zoom In/Scope time in this game is pretty long in general and especially for the sniper rifles even with stock upgrades.