The number of snipers on a team is irrelevant really, it still all comes down to skill and teamwork in the end.
If you have a full team of snipers and they are more skilled than the other team, or just work together better, then they will likely still win.
Even having one god like sniper can easily change the tide of a match, so having multiple snipers just means you’d have more people covering more openings. (plus a bunch of detectors covering the map)
The problem with many Vassili users (in my opinion) isn’t even that they can’t aim very well, as that part usually comes with practice… THE REAL problem is many sit waaaaaay in the back and don’t really see much action. You’ll get snipers basically defending, or attacking from just past where they spawned. They are usually defending the back of the EV, which is already the safest place to be.
These types of players will only occasionally see an enemy and not get many opportunities to actually anticipate when an enemy will be coming on screen, as it can be fairly spontaneous at times… where you have a clear shot of someone for like 1 second… then he is around the corner again. This usually ending up in making a panicked shot that ultimately misses, or in over aiming and missing your opening entirely. These same players often never use their detector, or don’t throw it far enough to do any good to anyone.
The best snipers are the ones that know where the choke points are and hit them hard… use detectors whenever possible in an area that is likely to have enemy player traffic, or an area that might be less guarded in case of an enemy attempting to flank. With a team near by to support a sniper, they are very lethal indeed
If you think about it though stacking any merc can be pretty OP in a way if you play to their strengths and coordinate well.
This rant is mostly pub related though, as its a very different ball game if you are playing a proper competitive match.