Rooster, I think you could make a good argument that Mwandishi and Crossings represent a extension of the "Evans-ish" musical ideas on Speak Like a Child and The Prisoner. Of course, by the time of the Mwandishi band, Herbie had "gone electric," so the connection isn't as obvious as it might've been. But listen to a tune like "You'll Know When You Get There" off Mwandishi. With a few changes in instrumentation, it could have easily been on Speak Like a Child or The Prisoner.
It's no coincidence that Herbie's Mwandishi band was a sextet -- more instruments for those Evans-like textures and harmonies.
OTOH, by the time of Sextant with Patrick Gleeson's increasing role in the group, I think that Evan-ish harmony thing became less evident. To me, that record feels very different than the two albums that preceded it. That's where I would mark Herbie's big stylistic break -- after Crossings but before Sextant.
Just my 2 cents.
I would never regard Herbie's music as over-rated. As a performer, he can be frustrating -- and I think I understand what people are saying about his perfectionism. His music sometimes feels dry, as if he's holding back. But, to this listener's ear, Herbie's music at its best -- and that's what we should always judge an artist by, right? -- is indelible, unique, transfixing. I love it.