I actually agree 100% with you, however I think at this stage of the market development, its enough to have a 3rd choice who's apps and services are open.
Librem is facing the "Grandmother problem". In order for this concept to actually succeed, it eventually needs regular folks to buy it. Its not enough to tell thousands of grandmothers to "buy our phone hardware and simply download and install any of the dozens of confusing and competing software stacks by following these 20 instructions on github". It needs to be marketed and sold as coherent integrated product, otherwise just buy an old Samsung and root it yourself....
I think it would be a huge mistake to NOT tailor a specific experience for a Linux phone since it would then be doomed to obscurity (more than just by fact of not being Android or IOS) like the million Linux desktop distributions that never "just get it" out of the box for 99% of people.
If all you want is a "Linux phone", you could buy a PinePhone for $150 or work on porting postmarketOS to an Android phone. The Librem 5 clearly has higher ambitions and could prove to be a more mass-market product.