My take on SACU upgrades is that they should work as either:
A) A viable progression out of t3 armies
B) A viable tradeoff from t3 armies as an accommodation to t4s
Either one of these solutions require them to work in tandem with t4s which should never really be phased out (they cost a bajillion mass after all compared to both rambo and t3 and are obviously a hugely enticing part of the game culturally). Also keep in mind most of the subjective terms of scaling here mainly refer to other faction's SACUs. They're just statements on where the unit's powerlevel should be compared to these units.
So in terms of design principles:
First I think all combat SACUs need to be REALLY bad at building. Like genuinely terrible. They can have the t3 suite, but the notion of their utility should come from "we can start projects but we need support units to finish it up." They should have the buildpower closer to something like a sparkie than what they are in this readjustment where they are still superior to t3 engies. If you want to have the utility of emergency t2 shields or emergency sams with your SACUs, you need to mix engineer SACUs into your combat group rather than simply spamming combat SACUs. It should be its own tradeoff. You can keep engineers at the buildrate set here, but you definitely need to nerf rambos because if you don't, it really hampers how much fun you can have with introducing different styles of gameplay per faction.
UEF Rambo should operate like a really heavy titan, it should be faster than t4s with short range but decent HP and alright dps. The goal is for it to escort the perpetually slow and not very impactful fatboy while being able to split up to cause damage and force T4s to either be out of position or slow themselves down in order to deal with them. This gives time for fatboys to do damage to T4s that usually can just walk into it while also giving fatboys quicker damage dealing potential indirectly.
Sera should have OC boys that get reworked OC to work like old OC. It should be a fixed cost with a fixed quantity of damage. I say this because I would rather OC be a prevalent part of the sera SACU experience rather than just having like, 2. If you have 5 of them, you do not want the volatility that comes with scaling E cost OC because it makes your own damage unpredictable and it's annoying as a user for knowing whether you can take engagements or not. I do not think it's an enjoyable skill gauge. So do something like 10k e for 5k damage or something similar.
Likewise, since sera has no RAS suite, it should maintain a high base SACU buildrate which in turn gives it a competitive advantage on top of OC in SACU fights because it will be able to build support structures much faster. This synergizes well with the fact sera SACUs are going to be encouraged to be a concentrated ball in order to do major lump sum damage to high priority targets of the enemy. This enables chicken to continue to be the sera unit for dealing with spam of units while the SACUs are there to prioritize targets that a chicken will have issue with alone.
Cybran have 2 t4s that really hate being surrounded. ML laser sucks really bad at targeting around itself and mega wants things to always stay right in front of it. So Cybran rambos need to be big on stunning, but not particular damage dealers. They would likely be the most utility driven of the SACUs but the worst in "1 for 1" combat. Make them fast, solid hp, good stun, but not great overall damage.
Aeon would just be an upgraded variant of the current harb + gc dynamic. GC is a tank that absorbs damage while harbs provide cheap but efficient quantity of dps while targets focus the gc. Aeon SACUs would want to be slow, slower than t4s. I imagine them as the inverse of UEF combat preset. They would be really good damage, great range, slow speed, and not good health. You want them to force engagements on your GC but you don't want them exploring the world without GCs.
I'm not sure what the exact values would be, but something like this would create a dynamic at late t3 stage where you have the options of
A) continuing mass scale of t3 units
B) transitioning to SACUs to assist your t3 army through their own individual utility
C) transition to T4 to accommodate your t3 army
Ideally super late land armies would mostly be consisting of T4 and SACUs, with t3 units primarily being there as a utility force.
