I tend to agree with your thoughts on Blue Note recordings, esp those from the 50-60s, but I have always liked this quality. Simple and direct with a minimum of manipulation. It has also allowed the sound to be 'improved' using modern technology. But, as you implied, the music is so great that to criticize it borders on nit-picking. On the other hand, some music is so badly recorded, that no technology can fix it. Motown is the most infamous example of this.
BTW, just rediscovered this one.
The First Esquire Concert
LaserLight 15 723
Recorded at the MET in 1944 (war bond drive)
Has to be the greatest Jazz line up for one gig in history. Billie Holiday in her prime is worth the purchase. Check it out. Sound is ok given the times.