> - rpi has GPIO pins
This is certainly one of the "bespoke applications" I was referencing. That said, I tend to feel that USB GPIO boards[0] are more capable and flexible when/if you need GPIO. There's also the ESP32 series which almost always make more sense for me at least. You can add as many of these as you want to meet any GPIO need you will ever have. In almost every case I've needed GPIO having it available over wifi vs being limited to a few inches from a Raspberry Pi has been tremendously more useful.
> - many rpi boards' max power consumption is around the idling power consumption of a pc, rpi zero 2 can run off a standard usb A port of a laptop
Fair enough, but how often does this really matter? I'm not advocating for unnecessary burning of the planet but as an example at $0.20 per kWh a seven watt delta comes down to $1/mo which (to me, at least) is nothing over the lifetime of the hardware when factoring in the dramatically improved capability.
> - rpi zero 1/2, rpi 3A and rpi 4 has usb gadget mode which means it can be plugged to a notebook and two machines will connect over usb ethernet. That is especially helpful for debugging headless machines when in a hotel room (no wifi under your control, no ethernet cable).
Another bespoke application that is perfectly fair. This can also be achieved with a tiny travel router (I LOVE mine) which will also run circles around gadget mode in terms of performance and functionality - significantly better Wifi, multiple real ethernet ports, it's own USB host for whatever. Running OpenWRT of course so it's still a Linux machine you can do whatever with - including connecting the USB GPIO boards I referenced above.
> - yes microsd is slow, but it's also cheap and easy to swap. That means you can: 1. if a board is broken then take out the card and insert it into another board. It will take you 2 minutes max and then everything will be exactly the same. 2. clone your entire microsd card as backup 3. you can swap different OS by swapping microsd. No need to partition your harddisk.
MicroSD is EXTREMELY slow and unreliable when compared to NVMe, microsd is cheap but you "get what you pay for". You can also achieve similar cost, swap-ability, and ease of overall use with USB flash drives which are often higher performance and more reliable anyway. A full EFI BIOS, bootloader, etc comes in very handy.
These are generally excellent points but the vast majority of Raspberry Pi use cases seem to be people looking for a linux machine/home server/etc that doesn't touch any of this functionality.
But hey, in the end use what works for you!
[0] - https://www.adafruit.com/product/2264