My first experiences with the FP2 were quite frustrating as well. Fairphone would just refuse to respond in any adequate way.
Never had any issues with my FP3, FP4 or FP5. Then again it’s not the hardware that makes most of the problems it’s the Fairphone support.
Could you not just repair the button yourself? From your description it’s not clear what the exact problem is but repairing a button sounds doable.
The following is not addressing how to rlace/repair the buttons of a FP5 but might be a good start still… (I will keep looking to find a more current repair guide)
And how much do they ask for the repair?