Not trying to change anyone's mind, just state my own take on the topic properly.
I thought game design is about making meaningful decisions and not picking the most optimal use of apm on menial tasks. Still trying to figure out what is "fun" in manual reclaim.
Also on topic but forgot to say, changing the gun range will also effect things like dealing with t1 pd, mobile arty, aurora, experimentals and telesnipes.
Back to the OP - I think gun is the more common choice just it feels more 'fun' rather than having a major advantage over T2.
I mean we have another thread running about how good tml is, and if you can use a few pd's to control more mexes they can start paying for themselves, as well as covering reclaims fields, etc. gun still needs e store and more power built to support it.
Recent balance increased t2 land speed and also added hotkeys for splitting units by tiers, so potential to divert your t1 spam vs gun ACU while your t2 units try flanking. Nerfing ACU range would be way too harsh at late game stage.
What would be a meaningful nerf to gun, would be to reduce the reclaim left by overcharging units, say half normal, then it is less punishing to lose your T2 units vs it
I'd argue that there are more cases of a unit performing much better when babysat other than the ACU. Tryharding with early raiding tanks and bombers is one. Getting the most out of your first strat is another, and a very impactful one. Hoplites and Mongoose. Beetles, by definition. Corsairs. ASF obviously. All differ from ACU with that you don't press 'O' before you micro. Singling out the ACU which you'll never have more than one of is silly. Nerfing the ACU and moving away from the original balance instead of removing auto OC (which moves us closer to the original) is sillier.
Nah, none of those units entirely end 1.5 (up to 2.5 if ur aeon) stages of game interaction in teamgames.
About nerfing damage of ACU:
I did some math for current state of game
Used UEF units as example stats. No regen, overkill, range, veterancy and unit loss taken in account.
Assumed 5s OC cooldown, 2 units killed by OC average.
Calculated price of ACU in units
ACU vs T1:
** No OC, No Gun: ~13
** No OC, Gun: ~18
** OC, No Gun: ~19
** OC, Gun: ~23
ACU vs T2:
** No OC, No Gun: ~3,7
** No OC, Gun: ~5,2
** OC, No Gun: ~9
** OC, Gun: ~9,8
So against T1 units Gun upgrade have almost same strength as enabling OC
Nerfing damage will impact T1 vs ACU
But against T2 units Gun upgrade is negligible compared to OC
Nerfing damage will NOT impact T2 vs ACU
What can be done to nerf ACU against T2 (without removing one kill OC and buffing it against T1):
@black_wriggler Oc mostly already kills reclaim, with its aoe even that of units that were not killed by it, Oc will never leave reclaim from t1 units and usually not from t2 either
Why assume 5 second cooldown when that’s only for auto-oc that I want removed?
These stats also don’t really showcase the reality that a gun ACU has continuous free value because the only time your calculation comes into play is if you have so many units that you can swarm ACU+its units. Most of the time, there is a very high margin of error that makes that infeasible and so ACUs get free value shooting at stuff. The point of the gun change is to make the margin of error tighter for keeping your ACU in an aggressive position.
@ftxcommando for simplicity. I needed some average value. Properly microed OC will be even stronger against T2 compared to T1
So to buff T2 against ACU we actually should keep auto-OC and remove non-auto-OC instead. 
I don't try to solve problem of making use of ACU riskier.
I try to solve problem of making T2 stronger against ACU without changing ACU vs T1 balance too much.
Free kills by ACU apply to T1 and T2 equally. OC and base gun have big difference.
The game isn’t a sandbox of 1 ACU against 20 tanks. Even then, I don’t understand why you did this via calculation and removed a variety of variables that obviously matter in game. You’re not killing an ACU with 13 tanks in a real game. An ACU is about equivalent to 20 tanks prior to OC or gun.
You can’t touch ACU hp without directly buffing every snipe tool with many already being powerful. So you touch ACU damage to make margins more punishing for keeping ACU idle at front unless you’re also willing to expend the time to micro it with OC rather than freely gain value by hitting the auto-cast spell button.
Your last statement makes zero sense. By making t2 stronger against an ACU you are by definition making usage of an ACU riskier.
So what actually you want to get by removing auto-OC or nerfing non-OC damage in half?
You stated that it's better chances of T2 against ACU. Neither of this really helps T2 against ACU.
To help T2 against ACU you'll have to really nerf overcharge.
But you don't want to nerf overcharge don't you? It's too fun to play.
By making ACU usage riskier, you open up more space for units to have value. Right now games converge to t2 all in or t3 rush because there is just such a ridiculous level of greed that is necessary to truly kill a player. You need like 3k extra mass in t1 spam or 5k mass in t2 spam to overrun an ACU with some vague low level of protection.
Attention is a resource and having to put attention on your ACU every 4 seconds to use OC means less macro means a loss in advantage that can help make spam more efficient as the attacker gets to decide which 4 seconds he needs to pay attention to front rather than constantly being aware.
Saying OC kills t2 is not news to anyone, I don’t get why you’re saying this. I am aware OC is insanely good. I don’t have a problem with it. I have a problem with it being strictly optimal to sit idle ACUs afk at 45% map control in every game with no actual drawback.
Idle ACU dies under 1k mass Cybran artillery in 12 seconds.
Or it's not actually idle.
You suggest to change game from "manage your ACU or die" to "micromanage your ACU or die". It's a bad change.
When he says "sit idle ACUs afk at 45% map control in every game" you should not interpret that hyper-literally to mean the ACU is literally idle even when enemy units approach.
He means you put the ACU at the front and you don't really think about it. You might make TMD or a shield or flak at some point and you might move it around or even give it a little patrol order or just walk it short distances now and then so it doesn't stand still and die to TML. He means you aren't using the ACU to push, you aren't retreating it, you just leave it at the front and don't think much about it. Not that its feet are bolted to the floor and it never moves at all.
TS stated in first post that he want to increase performance of T2 land against ACU.
Not make semi-agressive use of ACU you described impossible to worse players (like me)
Not nerf ACU against T1
I made math to check if one of his suggestions (nerfing gun damage) do help for this.
It is not but also greatly reduce chances of ACU against T1 land. To increase T2 land chances overcharge have to be nerfed instead.
TS don't like idea of nerfing overcharge. Instead he suggests to remove entire playstyle for not best players by removing auto-OC. That is how it looks for noob me.
Which in turn I don't like.
@tagada please also consider a nerf to t2 acu build speed to go with it, or some other change you think is appropriate, to make t2 pd creep weaker as compensation. With a nerf to gun range, the distance between pds can become much larger while still being safe, and on smaller maps, the early area control gained by such a strategy might become quite significant before a gun acu can muster a defense.