I'm not worried about the backup PG spot. I think Simons will be fine as a backup PG in spot minutes. Also, I think the teams biggest issue last year was their atrocious defense, esp at the SF/PF spot.
They've improved it.
And really not at the cost of the teams offense.
Now while the additions this year (healthy Hood, Covington, Jones Jr, Kanter and re-signed Melo) are an unknown for how well they will jell together, they collectively have potential to be significantly better than last years support (hurt Hood, Melo, Mario, Ariza, Tolliver, Bazemore, Swanigan, Skal, Whiteside).
Especially Mario, Tolliver and Bazemore. Good lord those guys were bad, especially Tolliver.
Combined those bums got the team 17 points between them, but I would bet they gave up more than they scored.
Even if the only changes they did was replacing Mario and Tolliver with Covington and Melo, you've improved the team a significant amount. Throw in Kanter and a (albeit probably rust) returning Hood and that's probably 5-10 more wins easily. Add to that a full year of Nurk (hopefully) and Trent progressing consistently, and it's probably another 3-4 more wins. So anywhere from 44-28 to 49/50-22.
Clearly, there are unknowns, but I think the holes fixed more than make up for the perceived hole at the backup PG spot. Before, SF, PF and C were their weak spots. Each one, at best, had 1 spot and no backup. And in the case of the SF, they really didn't have anything outside of Ariza, and while he was a blessing, he wasn't exactly consistent.