The real myth here is that the BIOS did nothing more than load 512 bytes and start executing. It was already doing tons of stuff to configure hardware and provide information to OSs well before UEFI came along.
The only thing a firmware really needs to is A) initialize RAM, B) initialize a display or serial port for boot comms, and C) load an OS. Anything else modern firmware does would be better as normal devices controlled by OS drivers without the ACPI/UEFI layer.
A third thing: it is of course super convenient if firmware provides some way to reliably identify the platform and provide data on devices that aren't connected to discoverable buses (such as bus controllers themselves), but even that's not really required. Linux lets you build a devicetree as part of the kernel.
And it's absolutely awful as an end user if you have anything even slightly unusual.