The one I have does burning damage, so I think it has a bit more effectiveness against robots.
Long range stealth: Overseers Guardian max damage modded w/ recon scope & silencer
Mid range stealth: 2-Shot Assault Rifle max damage modded w/ recon scope & silencer
Short-get-out-of-my-face-range: Mighty Combat Shotgun (+25% damage) w/ reflex sights, short barrel, no silencer
I realize the last 2 aren't true sniper weapons, but I feel these 3 weapons give a good balance for most situations for my sneaky/sniper character. Also carry a silenced 10mm if stealth holds and I'm close range. Really wanted that syringe rifle to be effective/useful for silenced non-lethal kills, but unfortunately I found it kind of useless.
Bloodwolf- don't worry about under powering yourself, if you keep playing you'll acquire all the power you need. I'm still playing my first character (over 500 hrs) and just hit level 52. I started with crafting, hacking, lock picking, charisma-type perks first. Then gradually added perks to the weapon types I liked the most (rifles & explosives). I got killed a few times, but gradually got better weapons and skills. I just enjoy the crafting and settlement construction/management more than anything. The game really lets you play however you want.
Anything ranged with "Instigating" in the name, because a Pipe Weapon can be made into an effective Sniping Rifle, and requires less Perks to fully modify. Another prefix for a Legendary is "Assassins'", because Humans are still the primary Opponent in Game.
Except for Ammunition use and the lack of a Silencer, a Six Crank Recon Laser Musket is a very dependable and effective Sniping Tool. I still use the Short Laser Musket acquired early in the Game, I have just kept it fully Modded as My characters build Perks. I like the Overseers' Guardian as My primary Weapon, but I do not modify it very much except for larger Magazine Capacity, and a Silencer
Yeah it doesn't really take people out very well, both damage syringes svck and the most straight forward long ranged killing syringe, the beserk syringe only works on very low level enemies, plus theres no such thing as a non lethal 'kill' in this game.
That being said, if you use the right ammo in the right situation for the right reason it can do awesome things, though much of its value tends towards short ranges.