The original Pi was an extremely poor desktop replacement. Both the speed of the processor and the available memory were barriers to running desktop applications. In contrast, the Pi 5 can perform acceptably for many applications while using mainstream open source software. I agree that the flagship Pi is no longer in its own original category. I would simply argue the category is defined by capabilities rather than price.
If you are interested in a Pi that is in their original category, there are options available.
The Pi4 1GB is $35. The Pi4 4GB is $55, and Pi5 4GB is $60 It is only the Pi5 8GB that is $80. The Pi Zero is even cheaper, $15 for Pi Zero W.
The advantage of the Raspberry Pi is the software. Raspbian just works and will continue to work. Other SBC might not work with their software and who knows if it will ever be updated. My understanding is that there are stable OSes for other boards, but then have to find boards that work.
I recently got Pi5 to use as computer, and microPC is probably better for that. But the Pi can be repurposed for other uses. I'm pretty sure I can pull the microSD card from Pi4 and put in Pi5 and it will just work. The Pi4, which is an awful computer, will do some thing that microPC can't possibly do.
Where do you live that you can buy Raspberry Pis at that price? Sorry, but last time I checked, either everything was out of stock, limited to single piece orders, or way above MSRP. When I checked the local marketplace (not eBay), people sold them for above MSRP, used! Imagine that. Used product for more than MSRP. In the electronics space. Crazy.
How long ago did you look? The Pi stock issues have been fixed since around the release of Pi5. Looking at rpilocator.com, everything is in stock.
I was looking at Adafruit where I could have bought all of them for the official prices. But can't buy more than 2 though. The same seems to be true of the UK and EU shops I checked.
Micro Center has them in stock but doesn't list inventory on the website. I was pretty surprised to see RPi0W 2s, 8GB RPi 5s, and a smattering of A, B, and B+ boards in the cabinet when I stopped by after the New Year.
RPi used to be $25 or $35 , and then use equipment lying around.
Now it's $80, plus high performance power, case, active cooling, storage, etc.
RPi is no longer in it's own original category. And when you compare via cost, it's a loser these days.
The only way the RPI isn't a complete loser is inertia, pure and simple.