My work pc is 8 years old, works flawlessly. Didn’t modify it.Not trolling. He said he could build a state of the art PC for under $3K that would last more than 7 years. That's just not true. You can't it. Sure I can build a really good one, but not state of the art. And, no. It will not last 7 years without significant reinvestment before that 7 years is up. Technology just doesn't work that way. Moore's Law and major leaps in tech will push things so far that it's just not feasible to expect anything to last 7 years. I have a 2014 MBP still on the shelf. A few months ago, I decided to see what it could do with a fresh OS install and clean HD. So I wiped it, installed up through Snow Leopard (for speed and stability), and put it through the paces. It was perfectly functional - at first. But, as you install more (and newer) software, updated Safari to it's most current version against the OS, and re-examined, I noticed that some applications wouldn't work and others slowed the entire thing down. It's still a serviceable machine and works fine for basic tasks and web browsing, but it's nowhere near the powerhouse machine it was back in 2014. That same scenario is exacerbated with PC's running Windows, especially as you step down in hardware specs.
As you said... a PC is upgradable, sure. But, at what point is it still the same PC? These days for serious PCs, the graphics card is just as (or more) important than the CPU. In your scenario, a ten-year-old PC with a NEW graphics card, NEW SSD, and MORE (NEW) memory would still "largely" hold its own. That's not a minor investment of a few hundred dollars. You're at about half the cost (or more depending on what you buy) of a new PC.
I have both PCs and Macs, and each have their advantages. But, to compare long-term residual value of a PC to a Mac is foolish. There's just no real comparison. One of my PCs is a 6th Gen Surface Pro with an i7/16GB/500GB SSD. It's great and probably the most used computer aside from my A1 iMac that sits on my desk in the office. But, in reality, I doubt that it will sell for much more on the used market than the 2014 MB Air with an i7/4GB/256GB SSD that my wife used until a year and a half ago.
Don’t get me wrong, I’d love to change it, I just don’t need to.