While I agree that having a good reference point that is prevalent amongst users as a baseline is great for reviewers. I also don’t think it needs to be one of the masses… “my” reference point for closed backs is the Elegia… “my” reference point for open backs would probably be the ZMF Aeolus… at least at this stage in my audio journey… personally I really enjoyed the 6xx and it was my first foray into “audiophile” level headphones and gear.
If we are talking about what “should” be the reference points that is another very subjective thing. Sure lots of people have heard the 6xx but should it be the baseline? I don’t know! I’m not even remotely qualified to determine that.
Another way of looking at it, is to state your preferred headphones and gear before a review to let people know your preference. Then they know you like a/b/c style of headphones or sound profile?
Another thing for me is I’m odd in that I can appreciate multiple different styles and actually prefer it… I don’t like being stuck in one sound profile for long periods of time (ADHD doesn’t help)