Single Page Applications were the wrong direction for us. Tens of megabytes of massive js libraries built using bundlers and minifiers and shims and whatnot, only to render something on the screen that would've been rendered with pure html using ssr.
Honestly I enjoy coding with React a lot. Components are a really robust way of reasoning about UI logic. But it's not worth the problems it solved.
The usecase for SPA's is really small. Maybe Slack should use React sure. But not all the other apps out there. Look at Github and Heroku. Smooth, beautiful and fast experiences. So reliable.
I miss the old days of Smarty + jQuery UI. That was a better direction.
Had we invested this much effort into that approach, we would've had a much better performing web today.