Facebook, Uber, TikTok, Snapchat, Instagram, Whatsapp, etc. None of them are optimized for Google index.
Most top consumer internet applications don't take place in your browser.
And I'd argue that google's about the only thing propping up the internet. Chromium's a reasonably open platform (certainly more so than internet explorer, which not that long ago looked destined to become the dominant platform), gmail has kept email viable, android is somewhat open (and without it, apple might own that space entirely), etc
Every other player that's gotten traction has set up a walled garden
In fact it's exactly the same reason why Mozilla is increasingly not sustainable. Email hosting is simply not a lucrative business. That's why it's all run by large portals like Yahoo, Google, Microsoft, etc. which use them not to make money but to collect information about people, and monetize through ads or other indirect methods. Of course, this only becomes profitable at scale, and there are not that many companies at that scale.
As for Mozilla not being sustainable: I think they could be, but not the way they run their business.
Email hosting is lucrative enough for Fastmail.
Fusing the two never seems to work well. See blog comments for an example.
Think about what would be left if you took away all "social" apps from the internet.
Even if we don't go that far, think about non-social online apps that don't use the "web".
For example, iCloud, Dropbox, Microsoft Office, Adobe creative cloud, etc. Most users of these apps use native apps instead of a clunky browser.
Some people think Microsoft Word is a clunky native app, others that Google Docs is a clunky browser app.
Maybe they are both right.
I would use Mozilla if the browser was just a little bit less bad. Currently it randomly takes me about 5 seconds to move my cursor in the hackernews input box. That is not Google's fault. Mozilla's future is mostly of their own making.
Using Firefox here with a few hundred tabs open, working just fine. I suspect your setup has other problems.