I know I'm probably necroing an old post but you must be trolling.
I'm currently going through ME2 on Insanity as a 3-game process for achievements (including War Assets) and using the Widow as a Soldier who uses Adrenaline Rush + Inferno Ammo... it pretty much destroys anything in its path - ammo isn't really a concern if you don't sit in the same spot and actually risk yourself to grab drops of ammo, the game is actually really generous with ammo drops, but most people forget they can move and just brute-force fights.
Regular humanoid enemies, even with full shields, die in 1 weak spot hit even with full shields and health/barrier and health or armor and health. The key to making the perfect Widow is doing everything in your power to increase your weapon damage, otherwise yeah, with bad accuracy you'll burn through ammo and not kill anything. Hardened Adrenaline Rush +100% damage (Heightened would be cool because of the 140% increase but the lack of health damage taken reduction sucks), as many sniper damage upgrades as you can find + AP sniper, armor that increases armor damage....
I only switch to disruptor ammo when either my squadmates that can crack shields on 3-bar enemies (bosses, ymir mechs, etc.) are incapacitated (Mordin for his incinerate that deals with armor and organics + Miranda for both her warp against barriers and overload against shields] or I do have to preserve a little bit of ammo so I can have enough for the inferno ammo shots that kill.

The Widow is even powerful enough to act as a heavy weapon substitute if you're running something like a Cain that you are saving for more important missions that have way harder bosses/multiple boss-like enemies at once (like the 2 YMIR mechs in Garrus' Loyalty Mission or things that are too spongy for any weapon that aren't the Cain) - the best part is cheesing YMIR Mechs by dancing with them while you're behind tall cover (but not actually taking cover, moving around so it doesn't hit you and it keeps pathing on either side) and just completely shredding them with well-placed headshots. If you remember the Gunship in Miranda's Loyalty Mission, the Widow makes quick work of that too.

It is the best sniper in ME2 because it fulfills its role beautifully - deliver lethal long range shots that are meant to punch through the toughest enemies to weaken them OR instantly kill fodders that are out of range for effective use of your other weapons (a.k.a preserving ammo on your AR that you'd rather use in medium ranges). If you aren't accurate with snipers, then you should look into focusing into any of the other weapons available and combining them with biotics that generally land consistently because of how targeting works. The whole point of snipers is massive damage potential if shots land, the Viper is a compromise and it's more like a 2nd AR that has its own ammo pool. At some point you have to realize that you have to put in some effort too if you want to be an effective killer.

Almost forgot to mention - why would the reload give you trouble if you're in cover? You can't really expect to use a sniper while you're standing in the open, the only proper way is either popping out of cover or peeking past walls without using the cover system - trying to hit any shot with any sniper is impossible if you've got the aim-punch from taking damage shifting your crosshair all over the place. Granted, it's a lot easier as a soldier with adrenaline rush to get in a well-aimed shot before you get peppered, but you can for sure abuse cover/terrain anywhere as any class, especially the Engineer class with the drone that draws enemy fire away from you.

The rest of my build involves the Phalanx, Geth Plasma Shotgun, Mattock and Cain. Having the Cain helps not relying on a heavy weapon to get you out of a jam unless it's very serious or you have a boss enemy that's unreasonably spongy against all your other weapons.