@Tex Yes, but then people also don't calculate the payback time properly either.
The delay isn't merely 10 minutes for payback, it is also the accumulation time.
So it takes time to accumulate the 6500 mass, then it takes time for the unit to pay back that 6500 mass. The total of that time, is how much mass is otherwise lost.
You can just as easily say it takes time to accumulate mass for mexes or for any other unit. The mass that you accumulate to build something and the mass that it has to pay back is the same mass. You even say yourself that it pays itself back in 10 minutes later on in the same post.
Maybe what you need and maybe the only change that is needed is for Ras SACu specifically to have an increase of their death explosion damage to 4000, so that like with t3 fabs if one or two die this will chain react and kill the other sacu near it.
This has been suggested several times in the thread but SACUs are really easy to keep alive. They have high health and regen and can build shields, and you can move them around. Adding a couple thousand points of explosion damage won't change anything.