Quote:
So there is plenty of justification to saying the maj7 chord is more dissonant than the dominant 7th.


I hear what you're saying but as a chord member the presence of a minor second/major 7 has to be weighed against the other intervals that make up the chord. When viewed in isolation a minor second or major 7th is of course more dissonant than a major second.

However in the context of Cmaj7, the effect of two major thirds a minor third and a perfect fifth between the major third third and the major seventh when voiced as 1, maj3, 5, maj7 effectively dilute the minor 2nd and make the chord as an entity sound like the resolution it most often is.

If it were otherwise the tension would require resolution to another chord and as you rightly point out it doesn't have that pull towards a tonic as it is the tonic in itself. Even if we have the minor second as the uppermost interval 1, 3 5, 7, 1 it still doesn't negate the the effect of the other voices.

Similarly when considering the dominant 7th as a chord remember also that as well as a major second it contains the all important b5th which gives it it's restless character, demanding a stepwise resolution to the third and the root of the tonic chord. It also contains successive minor thirds built on the major 3rd forming a diminished triad.

Alan