So Aimstrong, pretend SNF Season 5 was vcoh and you were in the finals vs DevM. You are both top of the game and sometimes it is THAT CLOSE that a luck roll can change the game. DevM went double sniper opening as Wehr and you go WSC to counter. You line up the perfect CS and your sniper misses his and his 2nd one in turn snipes yours. OK, so you just sacrificed time, MP, and fuel for the WSC and the one sniper which is now for nothing and most likely you just lost 5K+ in prize winnings. Sounds good?
It's a painful situation of course, but I feel that it is better than the alternative proposed here. I think the sniper doesn't fit well with the rest of the game and therefore can't be balanced properly, and that the 50% is the "least bad" option. Snipers, like mines, are necessary for game balance, but both of them are a bit out of place which makes them extremely hard to balance properly.
In the situation you mentioned there will be downsides for him to go those two snipers, allowing me to utilize my troops differently according to his unit composition. Negative zeal would help solve the problem, either by helping with my CS chance or by forcing him to spread his snipers, which gives me an advantage in not being countersniped back. Alternatively, with 100% hit, I would shoot his, he would shoot mine and he would still be one sniper ahead. Also, I can't speak for all, but I personally always made a point out of always trying to make sure my opponent wouldn't be able to shoot back after a countersnipe, by waiting till he had fired.
Would this be better? Being guaranteed to kill but also be killed? The US player would lose more due to the cost of the WSC building. At the same time, he should maybe not even rebuild his sniper, seeing as the WM player might rush vehicles for that occasion, forcing the US player to spend resources into AT weaponry after the botched countersnipe attempt. That way the WM player would still have sniper superiority. In the end, it's hard to say what would happen, as its almost impossible to factor map control into theoretical questions like these. A lot of other factors will influence the game at the same time. 50% chance to be hit is a boon as well as a curse.
I feel there would be many factors in the game that would change the dynamic other than the moment of countersnipe itself; lack of cap power, having stored a lot of his army value in two squishy units, the amount of shots being fired on regular infantry, two early snipers giving him a weak early army core etc.
With negative zeal only, in the situation you mentioned, his snipers could be covering the same area from two different positions, be placed at different parts of the map or on top of each other. If they are on different sides, the countersnipe will in effect be a 1v1 sniper situation. If they are on top of each other, I will be favored by having a higher chance to hit him while his 2nd countersniper only has a 50% to hit mine. If he covers the same area from different positions, then he has the advantage by having access to a countersnipe, and rightfully so, due to having invested more resources (2 snipers vs 1) into that aspect of the matchup.