I don't think we'll be good (much less great) defensively next season, as I see we'll be tanking next year, either through extending Lauri (thus having at least another safe year to do so) or trading him (thus sending us for two more years of real hard tanking where we'd be actually gunning for a 1st overall pick).
We'll be starting Collins at center, as his contract is too big for anyone take a bet on It next year, and he's also a worse PF than C (both ends of the floor, if anything, playing him as PF is one hell of a tanking move, so maybe we gonna go there), and going coach dnp on him would be terrible for locker room and the (already terrible) value of the last year of his deal (we didn't cut THT of our rotation till a third to half of this season for the same reasons while he makes less than half the money and may be out of the league next year).
I doubt we'll be playing Dunn above Sexton or Keyonte, even more If we don't trade Clarkson (which i guess we may do, but his value was higher this time last year I believe). Growth from Keyonte, Sensabaugh and Hendricks (and Kessler, but I don't expect him to do much behind/alongside Collins) could drive more winning, but better defense I only expect from Hendricks (even more If Keyonte be playing many SG minutes, defensively he's a PG in this league).
Also anyone we might draft this offseason shouldn't be expected to be a difference maker right out of the gate. And the only team in the conference that could realistically be up to tear It down this offseason is the Warriors (maybe the Lakers and/or Clippers, but these two I still believe they'll be going for It at least one or two more years, as the Suns and the Mavs), and maybe they'll just try to retool, all while Memphis should be up for a comeback year. All these things put togheter points to at least one extra year of heavy tanking, maybe two.