Without wanting to excuse the disappointing performance of the FP2, a couple of things that come to mind that may help getting more out of a phone:
Sounds like a connector issue rather than a battery issue. This is often the first thing to go (also on non-Fairphone devices), and why some people use magnetic connectors (examples) to alleviate stresses (especially an issue when charging from powerbanks on the go). If you find you run into this problem with different models, those connectors could help keep a phone going for longer.
Did support give any reason why they wouldn’t cover the new charging module, or was the phone already out of the two year warranty period by then? If the microphone on the new module was broken when you got it, why didn’t Fairphone support ship out a replacement - assuming you told them about it when you discovered the problem? Would be good to know what their comments were, as it may help others know what to expect from support.
Sucks that it takes that long. In the past Fairphone has mentioned being reluctant to hire temps when there are spikes in demand (in this case the FP3 launch), for ethics reasons and quality reasons, but try to manage support in different ways. Seems they haven’t cracked that yet.
Not that it’s any consolation, but they’re not necessarily trying to make an extra buck off the back of misfortune. The cost doesn’t add up to the sum of parts in the shop, as at the price they’re quoting they’re almost certainly replacing the core module, which isn’t listed in the shop (last price I saw for it elsewhere was €275 ex. shipping). In addition, part of the price will be labour and shipping costs.
You could be lucky and find that the issue isn’t actually the core - though changing the most likely modules with limited effect suggests it might be the core. Might be worth cleaning the connectors between the modules - but that won’t fix the no OS issue. Not sure what happened, not sure how to fix, sorry. ‘Not a valid USB device’ can be a number of things, including some that have nothing to do with the phone itself. There are folks on the forum who are better at helping you troubleshoot this than I am (and probably better than Fairphone support).
Home insurance may have options. Specialist insurance usually either doesn’t cover the issues you’re describing (for any brand), work out at around 30-40% of the value of the phone per year (i.e. cost of phone / average lifespan), and/or offer less than you expect when things do go wrong (think refurbished device of the same residual value with a high excess). For Fairphones you’ll likely have to call an insurer as the insta-quote function on the websites typically cover only the most popular models even for places that provide cover for ‘any model of any brand purchased in the UK in the last 6 months’. The last bit might be a key gotcha - could be that you’d need to purchase from a UK-based reseller (currently I only know of the phone co-op in the case of Fairphone).
This is a downside of 2-factor authentication (though the upsides outweigh the downsides). If the device is lost/stolen/destroyed, recovery can be a challenge. Apps will be linked to the device, though some apps like Authy lets you backup to the cloud. This still relies on SMS authentication to begin the restore process though, and a replacement SIM can still take a while to get to you.
Not using it despite it having wreaked havoc would be more of a waste. If it serves its purpose, just use it as long as is practicable. Fairphone still has the page up about the most sustainable phone being the one you already own.