but other phones have sliders or slots that will let you live swap either card without even taking the back off

Modern phones on purpose dropped SD card support but yeah, slimmer phones still have those sliders. To be fair you need a tool for that, unlike their option.

especially for a company that small

We really have to keep that in mind. When they planned the FP5 they likely had no idea Google would do the same. They take what Qualcomm offers, unlike tech Giants Google and Samsung that can basically dictate update lifespans.

relatively spotty history when it comes to patching

They are the ODM unlike GrapheneOS and comparing them to Google is really unfair. Google makes Android, so they know the code best. They patch very quickly, the updates work for their phones out of the box, less work for GrapheneOS.

Fairphone on the other hand has to maintain a unique device which is way more work, they get early access because of that though.

And their noncompliance with all the GrapheneOS security demands is the reason I dont use it.

seems to take issue with seem to be the LineageOS/Android defaults

Fairphone is Google certified and thus needs to ship unmodified Android including all the Google crap. There is a company called Murena that creates some hacky LineageOS-based OS and sells Fairphones with it preinstalled.

This /e/OS looks nice and has very nice integrations, but is fundamentally flawed and less secure than GrapheneOS for example (microG, depending on unmaintained apps, even slower updates,...)

even the fairest phone is environmentally costlier than rescuing an old second hand phone.

Regular phones dont get 8 years of updates so they will be outdated and should not be used. This argument makes no sense.

I got a used Pixel 6a with 2 years left, so used but way less long updates, so I hope on getting a used Pixel 8 which means roughly 1,7 phones instead of one, should be equally sustainable.