I think the improvements people hear are purely related to sound signature preference, some like the brighter T1 sound much more, and will define it as being better. When directly comparing the T1 to HD650, HD650 will lose, because it will seem muffled or too dark, although that's not true, and that feeling is only present for a short period of time before your brain adjusts from one sound signature to another. T1 gives an illusion of more clarity and/or detail when switching to it from HD650 . But thats not how audio gear is can be properly judged, its impossible to properly evaluate gear without long term testing. If I listen to both headphones for lets say a week straight, I like the HD650 better at the end of it. Its a headphone that hides its pro's and throws con's at you. Compared to many headphones even below its price range, it would lose in a A-B test, at least with most listeners. Beyer is the opposite, its throws all it has at you on the first listen, but with time it kinda becomes obvious its not as great as it first seemed. Clarity and detail translate into listening fatigue and annoyance, and lack of body in certain music. The over-exaggerated clarity gets frustrating to live with, a headphone so picky about the sound file quality can get annoying. It makes me personally choose the music I will listen to not by the music itself, but by the quality of the recording. That is fun for a while when critically listening, and in critical tests, T1 would win against HD650 in most categories, but when it comes to just pure music enjoyment, HD650 is the king. At least for me. Its a very polarizing headphone for me, sometimes I like it, sometimes I hate it when switching between headphones. But whenever I stick to it for a longer period of time , I just have a hard time finding a reason to own any other headphone. Its the ultimate hi-fi headphone, perfect blend between analytical and warm musical sound, an absolute best buy in my opinion.
+1 i feel you