N1b I can understand that, having been in that place myself. But while it's amazing to be able to update my Galaxy Note 2 that was originally supposed with Android 4.1 all the way up to Android 14 thanks to someone on the XDA forum, things aren't so great as a daily driver when you discover some things don't work, crash, etc. And the amount of backporting needed means this is a decent chunk of work to keep up with updates, not least updates breaking things.
From what I read on the FP forums their process doesn't seem a whole lot different. They do have access to the CTS so they can test better, but it seems that means they have to put more work in on every release to pass the CTS. Which may be why updates don't ship very often.
As a user you have to realize that this kind of 'best effort, you'll get an update if it doesn't break the build too much' is not in the same league as Google or GOS shipping Pixel updates every month.
TL;DR FP are trying to do a very hard thing with their update policy, and it turns out to be... hard. Credit to them for trying, but the reality is that they are actually getting a similar kind of update lifetime as budget phones. Like other budget phones, being positively surprised by the occasional update is nice, but it changes the value proposition.
If all you care about is the hardware then I have no reason to doubt their sustainability and repairability achievements. Just be aware that what you are getting has budget phone levels of software support.