By complicated, I mean that you have to modify your the default behavior of your host OS (which by default will grab any hardware) and pick a GPU that is supported by the guest OS. People with Nvidia GPUs cannot do that for macOS. Ideally, out-of-the-box, with a few clicks, most people including non-tech savy ones should be able to enjoy 3D acceleration in their VM, regardless of their host configuration.

Besides, in the long term, Apple is likely to drop support for AMD or Intel GPU in their OS (but yes, they might also drop support for virtio devices).

Yes, evdev is currently the best way to share your inputs devices to a VM, thank you for pointing that out (alas, it is only available in distributions with very recent virtualization-related packages).

In my (perhaps narrow) view: virtualization should be about making you less reliant on the underlying hardware. I wish that GPU manufacturers would agree on a common standard to allow users to split their beefy GPU into smaller parts (Intel is apparently dropping support for vfio-mdev (Intel GVT-d), adopting SR/IOV instead for their latest offerings. But SR/IOV is only available on professional models for AMD and Nvidia. In summary, there won't be a standard any time soon, leaving virtio-gpu as the sole hardware-agnostic contender)