This isn't a port of an existing driver. It's completely new Kernel space + user space driver. Of course it makes use of the mesa "framework" but that doesn't mean the driver is 27 years old.
What do you think porting a driver to a completely new GPU means? Doing so will require new kernel space and user space code. The existence of these new components doesn't mean there is a completely new graphics driver. Only parts of it that are platform specific are new.
The graphics driver of a system spans from a talking to the hardware to exposing a graphics API such as OpenGL or Vulkan for applications to use. Splitting up the graphics driver into separate components and calling each component a driver is different from what I mean when I am referring to a driver.
Mesa isn't a driver. Mesa is just an abstraction on top of the software that DRIVES the hardware (a driver), which is being written from scratch. Nobody (including the Asahi developers) but you subscribes to your definition of a driver. Drivers implementing Mesa may share next to nothing in common, so no, it's not a "port".
The ashahi driver inside Mesa builds upon Gallium3D so it does use shared components of the Mesa library stack. This is not a from scratch driver, it's one that uses the powers of the Mesa library.
