Personally, I dislike SCUs. They are just walking resource generators/engineers, and occasionally they suicide walk into your base. Seems silly, doesn't it? So I propose that we make SCUs unique... instead of making them do everything but crappy, we should make them do something no other constructed unit can do. I have two ideas:
First idea is to make SCU expensive, start with teleportation ability, and have teleportation work quickly. Teleportation is a huge part of the Supcom/FA canon and clearly it was intended to play a bigger role in the end game. Yes, this might make "SCU tele-snipe" a thing, but then it just requires balancing. No big deal.
Second idea is the make SCUs expensive and double as ACUs in the event of a snipe, in that you dont lose until all your SCUs + ACU are all deceased. Obviously, this would need to be balanced.
Personally, I dislike that SCUs are an upgrade to ACUs in nearly every way (all but overcharge) and would like to see them put on the same level as ACUs pre-upgrade (5000 mass cost, 100 DPS, ~10,000 hp, +1 mass +20 energy production). But that's unnecessary for the idea at large.