Why not? If the hardware runs an Amiga-like OS, it should be fair game to compare it with other hardware that runs Amiga-like OS as well. It's completely fair to compare it with x86 or used Macs as in the case for MOS. Once COS 2.x running on new Commodore Amigas are out in the wild, it's going to have to be able to compare with hardware AROS is running on, MOS is running on, and what OS4 is running on. That is a lot of choices for the end user to decide on, which is a wonderful thing compared what we had 12 years ago.
I take the point about about comparing AROS/AOS4/MorphOS on different hardware because when it comes down to it, you are talking about the actual computing experience and hardware plays a part the same as the OS and also the available software does.
But they are all Amiga operating systems.
At this moment in time, there is no justifcation to say COS2 will have to be able to compare with the above as there is no evidence to suggest it will be an Amiga OS.
COS1 on the CUSA C64 is Linux and will have to compare to other LInux variants on their
hardware
COS2 for the CUSA Amiga line might just be another Linux variant for all you know.