Good comment, @stuartk .
But, I think there may be some misunderstanding about modal Jazz. While it is true that the artistic impetus for modal Jazz was to allow Jazz players to “be less tied to chord changes”, as you point out, the players were “less tied to chord changes” as concerns the sheer number of different chord changes in a given composition. While a typical “standard” tune may have a different chord change in every measure of the tune, and sometimes even two or more in a single measure, in modal Jazz the chord changes happen much less frequently; typically every four or even eight (or more) measures. In some “modal” compositions there are no chord chord changes at all. The tune stays on one harmony for its entirety. Staying on one chord for an extended period of time the player is given the freedom to explore that harmony far longer than in a typical tune in which the frequent chord changes serves to “guide”, even force, the player to move in a certain harmonic direction while improvising. I think that this serves to give a feeling of “structure” due to its relative harmonic“simplicity”.