Just an observation really, but the dom7 chord is famous for having that rough coarse bluesy sound - due mostly, so I am told, to the fact that it contains what is widely regarded to be the most dissonant interval in all of music - the tritone. To my ear, the major 7th chord, by contrast, sounds beautiful and soft, with rounded corners. If it were a pillow or mattress, it would be the best pillow or mattress I ever had. It seems as if the dom7 and maj7 chords are on the opposite end of a spectrum. And yet, the major 7, in effect, trades in the dom7's extremely dissonant tritone for what is generally regarded as the second most dissonant interval in all of music, the minor 2nd (i.e., between the root and the 7th). So it surprises me that the dom7 and maj7 have such a different type of feel.

Just after I typed that, I looked more closely at the other intervals in these chords and can offer a provisional hypothesis. It seems that the maj7 chord has TWO of the most consonant interval - a perfect 5th (i.e., between the root and the p5th, and also betweern the 5th and the maj7th) whereas the dom7 only has one. I wonder if that could explain it.