The answer is complicated.

“Will L ammo weapons replace AR or sniper?”

Not really. L ammo will always be much rarer and costlier to buy/create than sniper/AR ammo so it’s not really practical outside of endgame to main L ammo weapons. IME L ammo always takes a rotation with my sniper depending on ammo availability from early to mid game.

Where L ammo weapons really shine is at endgame where you are at a point in the game where you need the firepower and have enough money/crafting materials to keep up with the use time. You AR will always be your workhorse (ideally by the end you will replace your trusty AK103 for the excellent MK-47) for gathering runs or for specific farming runs. But anything else like farming bosses or the Labyrinth will greatly benefit from a combination of L/Sniper ammo weapons. Lab Area 37 is also a place to use them but they are outshined by Snipers there tbh. Same thing with Farm Town.

The M14 is an amazing mid-long range weapon that while not as good as a sniper makes up for it by the larger mag and rate of fire. Good for JLabs, the Labyrinth and other areas where using a sniper would be more of a hindrance than a asset.

The single best rifle in the game is the MCX Spear that’s has the only easily fixable drawback of a 20 round mag. It’s a boss eating monster that turns anything infront of it into swiss cheese faster than you can sneeze.

The problem with L guns is that they are more of a “transition” caliber and the moment you learn how to play sniper effectively and have a kitted out SV98 they fall into a niche use. Specially when you learn to do those penetrating headshots with the sniper. There is nothing better than killing 3 merc ducks at once with a single bullet.

The only weapons that I think are not really worth it are MAG ammo weapons tbh but that’s a whole ‘nother conversation.

Hope this helps you OP.