The thread is about impressions.
And what better way there is to state your impressions, than by comparison?
In short, I believe it's perfectly appropriate to compare the HD600 to other headphones on this thread.
No, of course it is for that. More than this, it is appreciated to hear all opinions, whether of praise or criticism.
But I think in your case what seems odd is that you just joined the site one day ago, gave the HD-600 a run for a serious session or two, and maybe I am wrong, but you had several posts all about how inferior the HD-600 is. I mean, do I have this wrong: you literally just unboxed the HD-600, had a session, then made several posts about their shortcomings.
So yes, opinions are appreciated by everyone I believe, just please take the time to listen to headphones over longer periods of time. If you still feel they don't perform for you the way other headphones do, then that's the way it is. We all hear differently.