First of all, everything that is in the game should also be allowed to be used. But it really doesn't feel fair if your ACU gets mercied, especially if you had anti air with you.
So I'm absolutely in favor of changing the Mercy. I just don't like the change to the mercy in the current balance patch for the following reasons.
1. It is not true that the Mercy can only be used for ACU snipes
I mean, of course, that's currently the most prominent use for this unit. But in my eyes there are at least two more good use cases for the Mercy.
Catch some lonely T2 Mexes.
One Mercy is enough to kill a T2 Mex (except UEF). This is something Aeon can't do very well with T1 bombers and gunships, as they aren't mass efficient in one passing a single T2 Mex and it's simply too noticeable when multiple radar blobs appear. It would certainly deprive Aeon of an opportunity since they don't have a T2 Bomber alternative.
The desperate attempt to stop an experimental at the last moment.
Here I can also see a justified use case for the Mercy. The only real alternatives Aeon has in the early T3 phase are again T1 bombers and T2 gunships. Even if the gunship has an alpha strike, it must still shoot for at least 30 seconds to get the value of a mercy. Assuming you don't completely dominate Air to build 25+ Restorer or a CZAR, it could be a particularly awkward situation for Aeon to defend an Experimental just with T1 bombers and T2 gunships, since they are significantly more vulnerable to an even not too high number of Flak with shields compared to Corsair, Notha or Broadsword.
2. The new use case might be not so use full
So lets see what Aeon get's in contrast. The new Mercy will be changed to do AoE and damage over time weapon. This means that t2 Mexes can no longer be sniped by a single Mercy and there's really no reason to snipe an experimental anymore (except the Fatboy maybe) since the single targed damage is to low and run out off the AoE with ease.
So I see the new Mercy as a pure single use weapon for larger groups of T1 to T3 units, a bit like the Janus Bomber. However, the Janus is much better, as it is very good at flying into the opponent's base and taking out pgens, engis and other important things. Something that is unthinkable with Mercys.
And even against units themselves, I would always prefer the Janus, since it can bombard the units again and again and not just once creating one AoE from which the units could simply run out.
Also, it doesn't seem a good idea to me at all to use Mercys against units since they usually have AA with them and the Mercy may not even fire ones.
So right now as it is, the new design of the Mercy seems to me to contradict itself.
3. It's Buggy
When I tested the new Mercy, I noticed that in some cases the damage goes under the shield and can damage units below. I especially noticed that with the Fatboy who gets direct damage despite having shields on and dies with an active shield! in fact, 10 mercys can be enough to kill a Fatboy which is ridiculous.
4. Bad Visual Effect
Since the new Mercy now creates a poisonous fog, the fire animation was replaced as well.
unfortunately, one of the most pleasing visual effects has been replaced by an absolutely unrealistic looking effect. It just looks ugly when the Mercy turns suddenly into a poison ball, just like that.
So you replacing this effekt:
with this one (unfortunately it is not good to show in a picture what it looks like when the mercy suddenly becomes a ball.):
Some could argue that the visual effects are not that important. For me, however, it is and I really prefer to play a also visually nice designed game rather than an unfinished looking one. And I think it would also be good for casters and so getting new players into this game by making the game look as good as possible.
So what would I do differently now?
Basically I see two ways how the mercy cloud be changed.
The simple solution.
Halve or third the damage a ACU gets from the Mercy, so that it's no more difficult to snipe a ACU with Corsairs than with Mercies. Since ASF are now also getting reduced CZAR laser damge, I assume that the change also could done relatively easily with the Mercy and ACU. The Mercy would still have the use cases described above.
The more complex solution.
If you would change the Mercy into an AoE weapon, adjust the visual effect so that the mercy splits up as usual, but then spreads out into an area similar to the salvation. And give the "poisonous fog" also a bluish color and a stun effekt for a short time (fitting the fraction diversity) so that units get at least some damage before they can go out. or just remove the damage over time componenent and make it a single hitting weapon.
I hope this post was helpful and I'm curious what you think about the Mercy change.