Well I'll explain my understanding of why gpg balanced them like this then.
Sera's faction theme is around sieging from firebases, they have the best arty, shields, snipers, base killing units, etc. They are, in fact, the 'invasion' faction, or 'alien' faction.
Sera's mini ras on scus offsets the lack of ras while incentivising building them for general offensive purposes. You then use them to build sera's firebases or use their combat upgrades. I think they're supposed to be the focus of a late game sera t3 army where you have lots of t3 land units based around a sera scu. It's similar to how armies focus around the acu at lower tech levels, and the fact sera has an oc upgrade makes this especially obvious that they are like expendable acus at the late t3 stage. I'm not saying this is what people do, in fact, no one does or tries to use combat scus like this, but I think it's still part of the point of how they were designed. Anyway, I digress.
This hard pushes sera into an aggressive mode with their scus, with them representing and supporting sera's forward positions. They are the only faction with an aggressive faction identity, and I think it adds a lot of character to a faction made up of designated killing machines to have their scus focused around combat. It's consistent to the lore too. Think of sera scus as spartan warriors who only know war. I feel pretty bad for the designers when it seems no one realises what they were going for with the scu design or sera's design.
Why not just give them ras anyway? Sera acu has it, but scus already have mini ras. I personally don't want it, but there's enough people already saying how it's not necessary due to fabs. It's also just lazy and boring faction design.
If they did have it, I'd want them to have some energy based ras, say 5m, 1.5ke, and 10k storage. This would help sera oc scus, or they could convert the excess at a somewhat similar efficiency to the other factions.
Yeah I have nothing better to do.
TLDR: Sera is the alien faction.