Now my opinion : I am not in favor of just tweaking numbers and keeping the design as is, i'd rather see a rework of the unit. Current design has too many problems to be fixed with just small tweaks.
Now you guys bring up interesting point toward a full rework.
We talk a lot about frustration of getting sniped, but the frustration of using this unit is also very real, to the point where you never make it because it's too risky. I would rather have a weaker unit than a powerfull one that you can't reliably use. So for me the "1 HP, Low Fuel" aspects of the unit should just disapear. Higher HP (even if it's low) is a good step to make this unit more reliable. Bigger size, why not but what for exactly ?
Now based on what you suggest and on the last "AoE DoT" idea, i can see a design where :
- The goal of the unit would be to snipe isolated immobile targets such as buildings and to zone units. So it's not an ACU snipe unit at all
- The damage is DOT, so you can react by moving out of the zone or repairing the building being damaged.
- The aoe is large, damage small, but duration quite long, so you can use it to zone units off of a zone
- The mercy would be more "missile", and would fly in some sort of straight line, with little room to turn/ change direction
- Once the target is set and speed is max, it's hard to change direction, so it won't follow easily moving units. The payback for the mercy user, is that the mercy is harder to shoot at max speed.
Basically you would use the mercy to pick off isolated building like you would do with TML but here the counterplay is static AA instead of TMD. And the second (main) use of it would be to zone off units.
Maybe that's too big of a change, i don't know ... But i can see it being usefull and not too blatantly overpowered/frustrating to play against.