He's wrong about SEO being the differentiator. Quality matters.
It's a huge trope to think your product didn't work for the market because the marketers beat you. I used to be that kind of developer until I made some products that people actually wanted.
But he's right that the software market is changing. Software will be easier to build and require less people to build it. So more, smaller companies will compete for market share. Margins will be cut and the consumers will get more of what they want for a lower price.
I think this is called a working market. It's what it looks like when capitalism actually works.
This could be the end of enshitification.