Kelly; some of your comments are definately highly subjective - I've spent a great deal of time with most of the Beyer range and disagree somewhat.
I found the DT831 bass to be lacking in impact when compared to the 250 or 770, but definately adequate. Definately crystal clear and a little too harsh for heavy rock/industrial, but not
too bright (compared to, for example, the HD570). They're an ideal example of "how stuff should sound when done right" - but that's not what everyone wants.
The DT250 is a different beastie altogether, sure it's not as analytical as the DT831 and when compared side-by-side does tend to sound a little muffled or subdued, but listen for extended periods of time and you'll have trouble not enjoying your music through them - which is what it's all about IMHO. Smooth, enjoyable and forgiving while pulling the detail back a little and the fun factor up - the detail is there, it's just not in your face.
The DT770pro IMHO is pure enjoyment, I wouldn't recommend them as anything other than a fun and exciting headphone, the bass can be a little distracting at times and the midrange/vocals a little recessed, but if you just sit back with some good rock or impactful music they're an extremely enjoyable headphone. Stop listening to the headphone and pay more attention to the music and you'll be air-guitaring and air-drumming in no time.
Overall Beyers have their own special sound, not everyone likes the way they sound and each model sounds quite different, so while I personally don't enjoy the DT831, because they don't suit a lot of my music tastes, I can understand 100% why some people would like them - I found many tracks that were nothing short of magical on the DT831s.
Everything sounds
fun on the 250-80 while the 770pro is probably the Ducati of headphones - it's all about the ride and the feeling you get from it, not just about how fast it goes