As someone who has been writing code for 30 years and has been developing "web apps" since the late 90s, it's really funny to me how things come full circle.
You just described the entire point of client-side rendering as it was originally pitched. Computation on the server is expensive and mobile networks were slow and limited in terms of bandwidth (with oppressive overage charges) just a few years ago. Client-side rendering was a way to offload the rendering work to the users rather than doing it upfront for all users. It means slower render times for the user, in terms of browser performance, but fewer network calls and less work to do server-side.
In other words, we used to call them "Single Page Web Applications" because avoiding page refreshes was the point. Avoid network calls so as to not consume bandwidth and not make unnecessary demands of the server's limited computational resources.
Now things might be changing again. Mobile networks are fast and reliable. Most people I know have unlimited data now. And while computation is still one of the more expensive resources, it's come down in the sense that we can now pay for what we actually use. Before we were stuck on expensive bare metal servers and we could scale by adding a new one but we were likely overpaying because one wasn't enough and two was way overkill except for peak traffic bursts. So we really scrambled to do as much as we could with what we had. Today it might be starting to make sense to make more trips back to the server depending on your use case.
To address your concern about latency or outages, every application needs to be built according to its own requirements. When you say "there's not a perfect solution to this", I would say "there is no one size fits all solution." We are talking about a client / server model. If either the server or client fails then you have failed functionality. Even if you can get yourself out of doing a fetch, you're still not persisting anything during an outage. The measures that you take to try and mitigate that failure depend entirely on the application requirements. Some applications strive to work entirely offline as a core feature and they design themselves accordingly. Others can accept that if the user does not have access to the server then the application just can't work. Most fall somewhere in between, where you have limited functionality during a connection interruption.