@frogman
I noted a clear distinction in my initial post of “the ‘60s stuff” in regards to Lincoln. When I think of jazz vocalists, I think of people singing jazz music. I don’t consider the likes of the masterful pop songwriters I mentioned to be jazz. They wrote immaculately crafted 3-minute pop songs. They may be all fancy and stuff, with someone like, say, Ella Fitzgerald exhibiting incredible vocal prowess and improvisational acumen, but it’s often still fancy pop songs. She ain’t singing the likes of Parker/Gillespie/Davis/Monk/Mingus/Coltrane etc.
This is why I mentioned ‘60s era Abbey Lincoln as an example of a vocalist singing jazz music. Perhaps others may provide input in this regard.
That’s how I see it.
Perhaps, in apropos fashion, this could all be “boiled down” to a classic Gershwin line: “you say, ‘potato’/I say, ‘puh-tah-toe’”