For a fair fight snipers should kill with one shot to the torso at close range

Always 64 HP damage enemy loses when you shoot with sniper. Sniper has no strength . TTK is very bad 

I think the sweetspot is a really dumb idea that makes no sense, it seems an odd and artificial way to force sniper rifles to be useful only at certain ranges, making it too much of a situational weapon. And if the idea behind it is that it's a ranged weapon, then why don't they apply this logic to other weapons too then? AR's and LMG's are not designed for close range either, yet they deal their max damage and have the shortest TTK at close range but somehow that's not a problem, it makes no sense whatsoever. 

They should just make all sniper rifles have max damage at close range and gradually lose damage as range increases like all other weapons. Variety can very easily be made by having the largest caliber SR's lose damage slower and higher muzzle velocity, but have slower fire rate, whereas the smaller caliber SR's lose damage quicker and lower muzzle velocity, but have faster fire rate.

As for 1HK up to limited range and to limited part of the body, I don't think it would make sniper rifles OP as many seem to fear. It was like that in BF3 and BF4, yet I never saw anyone who could consistently dominate with sniper rifles at close range. Considering how short the TTK is in BF6 it would be fair to also have SR's be more deadly.

Even with a limited 1HK capability to the body SR's are still very risky to use at close range, not because of the damage but because of the obvious reason that it fires too slow, and missing the shot or hitting only a leg or arm will likely result in death against any decent player.

For some reason, those who oppose me think that everyone can quick scope. Not everyone can hit a single shot, and there's a 250ms delay just for ads. This is something that requires skill.

"Sweet spot" is a useless mechanic. There's no way to tell if an enemy is within range. 

Incorrect. If you're the one shooting, you can easily mark a point on the map and it'll tell you the distance to the target. It'll also work if you use other tools such as a rangefinder. If you are the one getting shot, if the sniper is in the sweet spot, the scope glint has a different color.

 Instead of sweet spot, you need a one-hit kill from the torso at close range, like 0-30m. So, it should be like BF3-BF4-BC2. 

Bad Company 2: I believe it had a magnum ammunition specialization that would increase the damage by about 25%. Allowing for one-shots up to about 40 meters in any body part, I believe? It could be countered by ceramic body armor. This made it highly inconsistent.

Battlefield 3: I don't remember sniper rifles having the ability to one-shot people at close range, but I could be wrong about that. 

Battlefield 4: It had 100 damage at 0 to about 12 meters before the damage dropped off. I might be off by 1 or 2 meters, but it didn't extend to 30m. As far as I can tell, the chest plate specialization did prevent you from getting close range kills, making it highly inconsistent as well.

It didn't really stand out to me as a proper way to balance the game. The idea that you need some sort of gadget to counteract the gadgets of an opponent just leads to inconsistent gameplay. It also seems quite strong to have a sniper rifle that's able to instantly kill people up to 30 meters. In the hands of a competitive player, that can easily lead to issues.

Instead I'd prefer the option of using a fast firing, fast ADS time sniper rifle, combined with fast pistol draw times. That way you can either quickly place a follow-up shot, or you can do the one-two punch where you hit people with a sniper shot, followed by a pistol shot.

Additionally, sweet spot mechanic that forces players to camping from a distance.

As we've seen in Battlefield 1, different weapons had different sweet spot ranges. You could easily make the sweet spot inside of a 80 meter range, where you're quite vulnerable to the other weapon classes. Don't get me wrong though, I don't particularly like the sweet spot mechanic. I think it's not particularly fun to be at the receiving end of somebody that just manages to kill you just because they stand at a specific range from you. 

This was my idea for the sweet spot mechanic. It rough but it removes the distance limitation. This will only apply to recon class

rather then using distance to activate it, how about adding it to hold breath mechanic. Simply aiming won't do, recon will have to hold his breath and hold for a brief moment when he feels the sight completely steady for the sweet spot mechanic to activate otherwise it will be a regular shot. (This will make sweet spots shots more deliberate and less trigger happy). You can still shoot as a trigger happy player but you won't get the benefit from sweet spot.

I didn't have the time to test this properly, but the M2010 ESR had a pretty odd damage model where it would do 64 damage at close range, but it would do more damage as you were a greater distance away from your target. In addition to that, it had a sweet spot at around 80-100 meters, where it would do 100 damage.

Well, if we are talking about a fair fight, then if sniper rifles should have one bullet kill at close range, it would by only fair that all other weapons, including shotguns, will be so accurate and effective on a long distance so they can easily compete with sniper rifles, right? ;)

With weapons, it's always a trade-off. Some weapons are better at specific distances or specific play style than others and I see no good reason why sniper rifles, already strong at long distances and headshots should have a role like a shotgun has on top of that. I however agree that the sweet spot mechanics is terrible and hopefully it looks like it may be gone in the last game builds (shown to streamers).