Apple Jobs/Woz dynamic
Jobs & Woz are the two poles of Apple.
Jobs wanted appliances and those machines built with guidelines are hard to repair, hard to upgrade not intended for either. Think of the original Macintosh, PowerBooks, and every non-high-end Mac since the Second Coming™.
Woz is a tinkerer and wanted expandability & customisation. Those machines built in his philosophy are the Apple IIs and most of the high-end Macs.
That the iMac was designed to be all but impregnable is not at all surprise. It is actually to be expected and avoided unless you want to play Apple^s very expensive game.
If you want an affordable, well-designed Mac that can easily upgraded, wait for the Mac Pros to go out of support, then they can be gotten on eBay for much less than £100.
Some years ago, I bought a 2008 Mac Pro for £30. I rarely go online with it and I use it for Photoshop and light video-editing work. It supports 64GB RAM, has 8x 2.8GHz Xeon cores and runs very nicely on SATA III SSDs in a RAID-I configuration. It is true that it could be faster and have a faster bus & RAM but for what I am using it for, it is more than fast enough. There is also a lot of software available from that period on the Macintosh Garden. And there is a lot of software there.
I have Ubuntu for Internet work (and to connect to the VM at work) and there is surely a version of Linux that'll run very nicely on that Mac Pro.
I am not a fan of Apple but I do like Macs and I don't mind waiting 10 years. The Macs, the Mac OS and the software that ran on them weren't too bad 10 years' ago.