RSpliet thanks for the follows up 
Define “durability” is a hard task.
After my experience with 3 different smartphones (Ace2, N5, FP2) my feeling is that repairability is not a key feature for a smartphone to be considered durable, in fact I have never broke a screen or needed to replace any parts. Maybe the battery could be the only exception, but I can’t be sure about it even if I asked.
What I’d like to see in a durable smartphone is the resilience to obsolescence: if I keep it with care and do my best to not drop it or get it broken, that phone should meet the expectations of me –the user– for a long amount of time. FP2 is simply not doing that: certain apps are not compatible, all the other apps are very slow and continuously crash. Tonight it took me almost 30 seconds to open a regular and plain SMS in order to read it. I have the feeling that this is not a problem of hardware, but of software. Apparently it is very hard to figure it out, but in the case it is true, then everything they say about a durable-fair-phone is just teasing.
I had a Nexus 5 that lasted 4.5 years (and did it way more better than my FP2 currently attempts to do now). I have friends with iPhones that made/are making them to last even more than 5 years and they are still able to use almost all of the most common applications that we need nowadays, without the frustration of wasting your time waiting for apps to open and operate.
I think 3.5 years for a mobile it is not that much, especially for a model as expensive as the FP2 was. Furthermore, FP2 was released in Dec 2015, which makes ~4 years today, but mine was already a pain in the ass earlier this year, which was ~3 or ~3.5 years since the release.
Coming to your dad’s computer, I have to say it’s epic!
However a similar case could be the one of only a few of us. Electronics at a certain point just reach their moment of obsolescence and they end their life. It is physiological as for anything on this earth (as you said). Nevertheless I think we should acknowledge the fact that for a so called “durable fair-phone” it is a little embarrassing to reach that point before the 4th year of life. It is not doing anything more than a regular mid-level smartphone, if not claiming to be ethic.
Supporting an ethic project is something I believe it is pretty cool and it’s the reason why, after all, I am still supporting FP (yes guys, in real life, with real people, face to face, I do not complain about the phone and explain only the cool things). They also have great recycle processes. So, at this point, why to focus on the modularity and repairability? Just make us a phone that resists to obsolescence!