Except there is almost nothing that an A-Wing does better than an X-Wing by the rules. The sensor range is really the only thing it has, and in that case something like the YV-560 would serve better (yes its slower, but it can double move easier with the higher strain threshold and has an even LONGER sensor range). For the same cost, which do you think would be more useful for scouting/run and gunning, 4 X-Wings paired with a YV-560, or 4 A-Wings. Keep in mind this is the same cost.
Keep in mind the A-Wing is supposed to be one of the most advanced Alliance starfighters. Its more expensive than an X-Wing to build. If the only purpose it had was as a scout ship, and it isn't even the best scout ship for the cost, why would anyone make one?
In an aerial combat scenario, sensor range is huge. The design of the A-Wing allows it to detect enemy fighters and then escape without engaging. It's possible for A-Wings to emerge at one end of combat, zoom to the other, eliminate the target (preferably a non-hard target), and jump to hyperspace. That's the point of them.
Is it going to be a huge lopsided thing? No. The advantage is going to be very slight. The A-Wing is competing with equally competent engineers from Sienar Fleet Systems. A reconaissance fighter is only going to have a slight edge over the competition, but typically that edge is enough to accomplish the given mission. This is true with any other fighter craft.
I think you might be inspired too much by RPS game design. Sometimes, there just isn't a counter to something, or things that fit neatly in a box. A fighter is a fighter is a fighter. The differences aren't going to be very large.