It also gives zero insight on whether grid storage, including chemical batteries, pumped hydro, or other is useful (yes), or economical (yes).
And caring about Elon Musk's opinion is foolish in the first place.
On a more serious topic, they seem to have their economics backwards a bit when it comes to battery prices. They say "And efforts to scale batteries on an artificial timetable drive up prices." this is a strange argument. While it's true that many people trying to buy batteries drives up the price, this isn't really a bad thing per se, since it will presumably by driven back into improvements in the production chain.