Seems like having an available 5% bonus on peak (!) usage is a huge deal, actually. Buffering shortfalls have an exponential frequency curve. I wouldn't be surprised if 5% extra generation would have been enough to cover, what, 60-90% of all brownout/failure conditions on the grid over the past few decades.
Also, too, it's a brand new technology just being rolled out, and building more capacity at the limits of factory bandwidth. You're acting like the number of powerwall users are all we're ever going have, which seems silly.
The baseline is not zero GW. If the grid planned for 35 to 40GW of demand for today and then sees 42GW load, the 0.125GW are over 5% of the excess load.
Serving baseline from batteries is unrealistic and will be for quite some time. Smoothing peaks or helping with unexpected high (or low!) load however is slowly becoming viable.
And solar was providing about 3GW less than it was about a month ago. Lower solar output but spiking fall temperatures. It's sort of a "coffin corner" for the state, currently.
I think they meant that if grid batteries are a good thing (which they are), then distributed batteries equal to 5% of their peak contribution, isn't nothing. (125MW/2751MW)
Also, too, it's a brand new technology just being rolled out, and building more capacity at the limits of factory bandwidth. You're acting like the number of powerwall users are all we're ever going have, which seems silly.