I think that is debatable. I'm not going to argue who is the better defender right now, because that is obviously Chief. But, I think the window for Dame (realistically given Nurkic, Collins, etc.) truly starts after next season. After next season I expect Collins to be up and running well, Nurkic to be a beast or be gone, and Oubre would fit nicely in that window.
What does Oubre have that Chief/Harkless does not? Better handles, in two years similar defensive ability. Oubre is just a more well rounded SF. You feed him the ball spotting up for three and he can either rise or go in for the monster dunk (around obstacles). Right now neither Chief or Harkless (who I really like) can do that.
My preference would be for Harkless to step up, work on his handles and driving, and take over the SF spot. I think he has everything we need at that spot if he could handle and drive.
BUT (big BUT), I also think that Olshey has to prepare for a future where Dame/CJ never get over the top and in 2020 or so, the team decides it just isn't going to happen and it's time to rebuild on the fly. At that point in time I really like the possibilities of:
Simons, WBIV
Trent,
Oubre, Harkless
Collins, Biggie?
Nurkic,
And whoever we pick up along the way.