It's highly unlikely Apple is going to support discrete GPUs in any ARM-based Mac without another major change in business direction. So once the full product line is available, it's going to be as Oranges-to-Oranges as you can reasonably expect.
An M1 Mac sees and mounts a discrete GPU connected over Thunderbolt. It just doesn't have an ARM flavored driver for it.
Which seems to align just fine with Apple's ongoing efforts to get rid of all the kernel mode drivers and replace them with user mode drivers over time.
I don't think you should read too much into their entry level chip not supporting external GPUs in the first generation.
