Re: " it's moot to only talk about what professionals and enthusiasts use PCs for."
and not, for example, that PC sales reached saturation and replacement cycles got longer (especially since SSDs gave a big speed boost to machine that were only I/O bound).
^^^ this ^^^
I have a 2010 era iMac (2.93GHz i7) that I fitted an internal SSD to as the internal drives are a PITA and it's pot luck which manufacturer you get - I lucked out and got a Seagate which naturally shat itself. That machine is still good for whatever I need to do computationally over 7 years later.
I built a replacement and the end of 2017 for 2 reasons...
1. Tax deductions - may as well have something for the money as it'll be leaving the bank account one way or another.
2. NVMe drive and USB 3 as well as the ability to stuff it full of drives and RAM and easily replace any parts that fail.
3. Heat dissipation when under heavy load. iMacs aren't great when under stress in a hot climate.