Comparing the sniper to the infantry(man) is like comparing the field goal kicker to the lineman. One is precise and effective but never holds ground, the other keeps what he steps on.
The roles of the sniper in recent past and today are mostly about intel and interdiction, not defeating the enemy. Intell about high payoff targets, enemy formations and activity behind the FLOT (front line of troops)/in the deep battle territory is invaluable to the major commands in the that area of operations.
Interdiction, long having been a single shot well placed to disrupt an enemy command ( usually company or higher grade officers) then silence and evasion, has morphed into a more local overwatch from a key piece of terrain and mostly in urban terrain to protect ground missions from ambush. Often infantrymen/sappers/MPs/EOD etc know that while they are the big ticket operation, they also know that the snipers in overwatch consider them bait to draw out enemy marksman, having been in both roles.
As far as the efficiency comparison between the two- that is a silly comparison. The sniper may kill a handful, while expending a few rounds or calling in indirect/CAS etc, the infantry squad or platoon ( the fighting elements of the US Infantry) are designed to find, fix and close with and destroy enemy formations much larger than themselves to obtain a tactical advantage- in other words take ground away from the enemy while killing them in the process.
The sniper has the luxury and indeed, requirement to carefully think out each shot and its effect on both the situation in general and his team in particular. He disrupts and hopefully evades the subsequent search and destroy missions that inevitably follow his shot.
Having served in both roles during my enlisted years, I can honestly say that the value of the sniper is great, but not at the expense of the Infantry squad.
One problem that the Army and Marines have been addressing is the need for more precise fires at the infantry squad and platoon level. The US Army Designated Marksman Program emphasized the application of accurate rifle fire out to 600m using upgraded M16A4s or variants. The Marines do similar and both have seen great benefits of having not only better marksmanship training, but also better infantry squad weapons that are designed to hit at mid range.
Snipers in the Army Infantry Division used to be six two man teams per light and airborne Battalion, compared to 36 twelve man squads, and 12 heavy weapons squads in the same battalion. Not sure what the TOE is today.
Finally, the infantry squad moves into enemy held terrain with the intent of making them respond, so volumes of firepower is required to overwhelm the usually larger better defensible enemy unit ( inside hard buildings, behind barriers etc, so suppressing them while another squad maneuvers to a flank is well, an absolute. The sniper bides his time and only enages when all possible variables are in his favor ( in the deep aspect) while he fights from a prepared, protected position in the overwatch mode.
Don’t compare the grunt squad with a sniper team. It is disingenuous and not a valid comparison in the least.
The dismounted trooper or Marine (infantry or otherwise)ought to be the most respected warrior in our nation. They bear the brunt of the fight, do the super majority of the heavy lifting and face the most uneven odds, (in my experience as both an enlisted infantryman (83-92) and as a commissioned combat engineer (93-07)).
When I was a young enlisted Marine, I was assigned to guard our sniper. He had a Winchester Model 70 in .30-06 and he was an outstanding shot. We would move out together in the predawn dark and he'd pick a hide position while I covered the "back door" with my M-14. As soon as he got somebody, we'd get back to the company perimeter as fast as possible.
He killed a bunch of NVA and once he got what we believed to be a Chinese advisor - but honestly, our company was effective and deadly, day after day.
Snipers are just a tool that you use to add to the battle.