I would agree... the HD650's before the mods and burn in, and with the wrong set up, sound muffled, foggy, and lacking in detail - I'd have sold them a long time ago. But... "persistance pays."
After all of that... they're a dramatically different headphone - sounding almost identical to the RS-1's, but with a bit bigger sound, and of course just a bit more impact. PRAT, clarity and detail are no longer an issue... and of course... mids "to die for."
If you haven't heard them in that context... you haven't heard them.
I still like my RS-1's, maybe even a slight bit better (just a very, very slight bit more clarity and detail)... but... my HD600's and HD650's have been "transformed" - quite literally.
Now... is it easier to just buy some phones that don't need all of the tweaks of the Senns - certainly. But... then do you have the great impact and the forward mids of the HD6XX's, or the RS-1's - I'm not so sure. If you want "realism" and "emotion" in your music... all of these phones are hard to beat. It's a lot like comparing Maggie's to any form of box speakers - there is no comparison... in the speaker-world anyway (with the exception of other planars and electrostatics, of course).