Alright, you bothered me enough with your garbage posting.
There are two ways to make a viable ACU upgrade: either it (1) answers a problem proposed by the baseline gameplay of ACUs or (2) it solves a weakness in a faction roster
Sera resto field sees use because it give’s survivability to a mid game push to a faction that gets their survivability option at t3 stage. Sera nano is more expensive and therefore better because their other midgame survivability option for a push is to facetank with ACU so that the handful of ilshies and legion of zthuees are unimpacted by enemy long range fire + ACU.
Sera double nano and double gun are no longer “good” because they answered an old problem: sera t3 stage being horrible and them needing something to hold the line until t4s can get churned out. Or being a more extreme facetank for their terrible othuums. Now sera t3 stage is quite solid so the upgrades are simply “fun” rather than an interesting choice to consider.
Billy answers a UEF problem of dealing with a t4 push combined with t3 support. You billy the t4, support dies, now the percies solve the t4 problem.
Cybran stealth was buffed to become an answer to (1) because Cybran ACU had no way to compete with every other faction in mid game survivability. Now their stealth upgrade went from simply being a unique tool to being a solution to (1) with a unique flavor, same as UEF nano or Aeon shield.
Aeon gun range was unique because Aeon t2 stage used to be horrible. Their ACU was solving (2) by becoming their t2 stage answer and it was up to the Aeon player to build up an advantage at t1 stage to then be able to quickly transition to their extremely strong early t3 stage for a snowball.
Now Aeon t2 stage is extremely good. Now their unique ACU doesn’t solve a problem, it creates one for every other faction. There is no hole in their roster that the ACU upgrade fills it just makes a strong stage of their game into an oppressive stage.
Now could you find another thread to ruin with pointless garbage so I can read an actually thoughtful post? I guess it was my fault for assuming I didn’t need to spoonfeed basic game interaction, but it is a public FAF discussion so my bad.