Was told by third party installer that whole home back up without soft starts or the Lumin would not meet the design parameters and wouldn't be approved.
My ACs are old (2005) with very high LRA.
Hmmm, have you tested whether your Powerwalls can start your ACs (with the utility turned off)? I can see why Lumin would solve a pragmatic problem of your ACs being more carefully managed so they only turn on when you're ready for it with smart load center management. But I don't see how Lumin solved a code compliance problem.