When you take this into account, Ballads is an amazing achievement by a working quartet that was firing on all cylinders:
from wikipedia
Critic Gene Lees stated that the quartet had never played the tunes before. "They arrived with music-store sheet music of the songs" and just before the recordings, they "would discuss each tune, write-out copies of the changes they'd use, semi-rehearse for a half hour and then do it". All the pieces were recorded in one take, except for "All or Nothing at All"