DX to me is reduced cognitive load. We are all operating at the limits of abilities, better DX expands the scope of what we can accomplish in our weeks and months.
Often things sold as DX are absolute garbage dead end schlock, like a Flash to iphone app builder or something. So I get some of the indifference (google's not yours). But I don't think we should think of it that way.
Just on your last paragraph, I think it started that way. That Firebase would be the competent general problem solver that you might need to break out of. Firebase and App Engine have tended to weaken over time, so that you needed to move to GCP more often. Ideally Firebase would get more powerful, cover more cases, and have higher quota limits. Instead it feels like they are being degraded or abandoned rather than embraced.
I've never gotten the impression that at google DX was lionized. Examples of doing this well culturally are pre-Salesforce Heroku, Github, vscode, and Stripe.
A github/heroku style culture doing GCP would crush all competitors. Instead if anything GCP is a little worse than AWS.