Proposition, remove SACU upgrades entirely, instead have a selection of uniquely balanced units for different intended roles.
The main reasoning for doing so is simple, it would significantly boost freedom to tweak and balance each type of SACU. For example, instead of having to give every SACU the same base movement speed and the same upgrade giving the same regen boost, one could easily choose rambos to move slower but have even higher regen, support units to move faster but have slightly lower regen, or any veriation their of.
As a secondary benfit, it also streamlines and standardizes the process of picking and building units, making it fit the already well established methodology used in all other factories.
Besides, there is never any good reason to go and get, for example, a ras preset and resign all the upgrades into a rambo. Just go and build another rambo, it would be faster, cheaper and easier.
Ok thats the big thing out of the way, now for smaller balance details.
UEF engineering upgrade is largely redundant. If you need lots of build power over long range, build kennels. If you need the ability to start building t3 buildings anywhere on the map, just use a transport to move t3 engies or the SACU its self. If you do want to have the SACU to have engie drones, then at least cut it down to one upgrade teir instead of two.
I am all in favor of faction diversity, but in this exact case functionality has been sacrifeced to for the cause.
The base stats of unupgraded SACUs are absurdly high. This was fine before, but now with the intention of lowering them down to fit in with t3 land, being able to build a non experimental unit with a hp over 15k and high regen ontop is excessive. Additionally, the fact that only Aeon SACUs can be one hit killed by overcharge is a bit unfair. Lower the hitpoints of all factions unupgraded SACU to 15k or less.
Remove Aeon sacrifice upgrade and instead give it as an addition to the engie upgrade for no extra cost. Sacrifice is simply way to neiche to justify its existance as a seperate upgrade, ontop of being largely redundant (Two mutually exclusive construction upgrades, just why?)
Buff or replace seraphim SACU TML upgrade. Getting SACUs into play happens much later then getting T2 TML laucnher meaning its much eaiser to counter SACU missiles, they also cost significantly more to build and are semi redundant because you can just use the SACU to build TML laucnhers anyway. As it stands they have very little reason to use instead of other options.
I prepose a few possible changes:
Massively boost the range of the SACU TML so that it substantually out ranges T2 TML.
Buff stats of the TML projectile to differenciate from the t2 version (More missile hp, faster travel speed, larger AoE, EMP effect, stuff like that)
Replace the ability to build TMLs with a MML weapon, kind of like a land equivilent of the seraphim crusier.