Agree that you'd rather take a Jayson Tatum than a Marcus Smart or a Jaylen Brown...but they're all good players, even if only one's a true max/franchise guy. Similar deal in Phoenix, where Devin Booker's the marquee young'un but Mikal Bridges (10th pick in '18) is a key defensive cog/complementary offensive piece.
If you look at those secondary dudes' freshman year shooting numbers, they're all of a similar profile:
Marcus Smart: 29.0 3PT%, 77.7 FT%
Jaylen Brown: 30.0 3PT%, 65.1 FT%
Mikal Bridges: 29.9 3PT%, 78.7 FT%
Isaac Okoro: 28.6 3PT%, 67.2 FT%
Hopefully, Okoro converges on a best case, Brown-esque outcome. I do worry a bit that the Cavs will panic if his shooting seems to be getting in the way of winning, but their (lack of) FA moves suggest they aren't really in a rush to maximize W's.