How is it that my modded laser pistols are better at sniping than actual sniper rifles?

You mean laser vs balistic? I would think laser beams would be pin point accurate at any range bullets take in to account distance gravity or friction..or velocity...all the physics stuff. Though if someone was wearing mirror armor would lasers bounce off? Mmmmmmm

Either... Even laser pistol vs laser sniper rifle, the pistol is still better from a distance.

I worked out very early that there is no point to scopes. I've been using reflex sights because they don't wobble like scopes do. As long as you can can see their head you can headshot. The most damage comes from perks, so rifles do less damage than pistols is you have more points in their perks.

While I have not done extensive testing, I have not had difficulty sniping with a .308 pipe pistol (gunslinger char) nor .308 or .50 Hunting Rifle or a Laser Sniper rifle (Rifleman Char). I hit what I'm aiming at so I don't see the problem. I will admit I have never set up a Laser Pistol for sniping but if it's simply a numeric range issue, that would be an interesting point to discuss. I certainly have not seen anything that makes any of them more accurate than others (and I'm assuming we are discussing sniping out of VATS).

Scopes are of use at extreme range, but get in the way if the target is within a certain distance. The range stat on guns is actually relevant. You start doing less and less damage as the distance to target moves beyond the gun's range. My go-to pistol is Deliverer, and while I can, if I'm careful, make certain headshots with it against still targets, the distance is such that the damage isn't worth it. Then there are targets who are so far away that it's simply impossible to reliably land a headshot with only iron sights or glow sights (the only options for Deliverer). Hell, sometimes there are enemies so far away that you can't reliably hit the target at all, even in the chest. In these scenarios, scopes are invaluable.

I'm using a laser rifle for my current sniper and I've found it's not THAT much different of an experience from my other build using a .50 caliber hunting rifle, with a few exceptions:

1.) Recoil and Accuracy. The recoil is slightly better on the laser rifle, but the accuracy is worse. I always headshot enemies from ridiculous distances with my .50 caliber, but I find myself missing my shots a lot more often with the laser rifle. Alternatively, my .50 cal takes significantly longer to readjust than the laser rifle. So it's a matter of preference and opportunity on that front.

2.) Range. I talked about this in the point above, but the range on my .50 cal is insane. I can barely see the enemies sometimes, they're that far away, and I'll still successfully headshot (or at least torso shot) them 9 times out of 10. The laser rifle, on the other hand, becomes even less accurate the farther away I am. The stats on my laser rifle say that it has better range and about the same accuracy, but in my experience, the .50 caliber was better in this regard.

3.) Damage. My laser rifle is WAY overpowered compared to the .50 caliber. Even without sneak modifiers I will tear through enemies on normal mode. My .50 caliber takes at least 2 shots on harder enemies, and by then I've lost the element of surprise.

4.) Fire Rate. The laser rifle can fire much more quickly than the .50 caliber, and I can easily hipfire at a charging enemy in a pinch. The .50 cal, because of the staggering recoil and less damage points, has me switching weapons much more often. And while that helps me to experience more weapons and makes battles that much more exciting, sometimes the buttons are tricky or there's no time, and I'll have to sprint away.

These are all I could think of at the moment. There's good and bad for both. It all depends on playstyle. I myself have had a more successful sniper build with a ballistic rifle, but that's just me. Especially since you can muzzle it, even though it reduces the range a bit.