Heya,
That's the thing, I don't think they're miles ahead. I think they're ahead, but it's not a margin so great that if I put them on my friend's head and ask them to rate the sound quality from 1 to 10 after 1 minute of listening on three mid-tier headphones and one high-end and see just how well they all correlate high quality sound to the high-end. I find it to be just another headphone at this point, but it's one that does the things that I wanted. I can definitely see how people would want the T1 over the HE-500 if they're into treble. I already feel like I've lost that bright sibilance free high of the SRH940. But, I still have great treble, it's just a bit smoother, which is actually really pleasant for long listening. I have great mids. The kicker is that I have serious bass attached to it. Most headphones that I've tried that have great bass, usually have recessed mids or have a veil of some kind. The HE-500 doesn't. It's got great bass, great mids, great highs, but nothing is veiled, and at the same time, it's also not so sharp and shrilly that it cuts you in half. I think a lot of the sound quality, for me, was actually more about finding a frequency response // sound signature that did what I wanted for all genres. That was incredibly difficult to find in the mid-tier headphones. The HE-500 does that across the board for me, as it's capable in all regions of the spectrum.
When I put it up against a mid-tier headphone that is similar, there's always something missing. DT770 felt like it wasn't going as low, mids were not as present, highs were less smooth. K701, missing bass. SRH940, missing bass. PRO900, missing mids. DT990, missing mids, bass not as low and controlled, highs not as controlled and sibilance free. HD580 (HD600), veiled, not energetic, bass didn't seem to drop as low. Then there's of course sound stages and imaging. They all sound really good. It's just they didn't do all of the things I wanted at the same time. So I had to have a different headphone for a different purpose (and some just to test of course and for fun).
Very best,