Well the SCSI PCI cards came whit ROM that enabled you configure and boot from it, as for graphic card this where pretty standard, booted into text mode, simple design but it worked, I think this was possible on ISA too, this was true Plug&Play.
What Microsoft later called Plug&Play was nothing more than drivers included on installation CD, and also ability to download drivers from the internet, of course never worked, as Microsoft even to this day, has no vendor drivers on their servers, and you have to look for product and vendor id's, to identify the products you have in the computer, and Google your way to the right drivers.
Autoconfig worked because it worked like PCI/MSDOS, roms where filed whit needed drivers.
As for PC CPU's they were seated in socket, so you can replace you 486SX whit 486DX, and you got small book describing how to set multiplayer and clock, it was easy, and sheep compared to this custom build accelerator boards or Amiga.
I agree however that configuring memory on PC/MSDOS was hell.
Base mem, EMS, XMS, and high mem, and upper mem, really hated that.
Having to disable the CDROM, and mouse driver or load it up in high mem to get enough base memory to load programs.
