I guess you should like https://sxmo.org/. I really hope it can be ported to Librem 5 at some point. The website is down, so here are alternative links: Sxmo - postmarketOS Wiki and https://web.archive.org/web/20220127122917/https://sxmo.org/.
The problem with your “simple” solution is that adding existing apps is super-simple and many users would notice it and benefit form it, whereas “fixing the basic functioning of things” is the hardest and most time-consuming part.
Isn’t iPhone’s interface designed in the US? So you have any links saying otherwise?
Software will be fixed at some point. Hardware can’t ever be. Purism chose the long-term strategy, and I agree with them.
In fact, it does not come with Firefox. It comes with Debian repositories and you can install Firefox from the command line AFAIK. Using Debian saves a huge amount of time in the development, but it does not have to be the final destination (see SXMo).
Most people can’t live without a browser on the phone. Firefox is the most privacy-conscious browser among the existing (well, maybe GNU IceCat is better).