The issue here isn't that the California power grid has deteriorated, but that there's an extraordinary heat wave. I don't think it's fair to tie this into a grand decline narrative.
It's hardly conclusive for a "grand decline" narrative, of course, since this is just one anecdote for an entire society.
Also robust grid which enables selling back to the grid would have helped, such extreme hot weather goes in hand with solar generation
The load shedding occurred around 8-10pm after the sun has gone down (but while it's still quite hot) so more solar wouldn't help much.
[0] http://www.caiso.com/TodaysOutlook/Pages/supply.aspx and select 9/13/2019 [1] Same as above but select 8/14/2020.
I've read some predictions that suggest these heat waves becoming a regular thing could happen within the next five years, but I'm sticking with more conservative predictions.