There are multiple issues there. There are only so many minutes to go around. For example, add another PF rookie, and there likely won't be enough time for the rookie, Chriss, and Bender. Add another young PG and there won't be enough time for either him or Ulis.
You have to be able to develop young players, and that takes playing time.
Then you have the matter of extensions coming up at the same time. Players may not be happy with their playing time, or you may not be able to afford that many extensions in a short time frame.
It really is not as simple as, "Add a bunch of young players."
I agree it isn't ideal. But then the league isn't ideal. It's a 2 and half horse race. And if we can't butt our way into the fray, get a young talented core who'll be ready when the window opens. I mean what's the formula nowadays: either land Lebron, or nail 3 draft picks like Steph, Klay, and Green which lures title hungry stars like Durant. The latter is all we have to aspire to. So invest in scouting (McD totally has done a good job of this) and pray it pays off.
In the meantime, I'm not really interested in watching a team that has a bunch of middling players who offer zero championships and keep us at the latter end of the lottery. I'll take an up and coming team that drafted well, with guys we can root for (ie. NOT M. Morris), and are building chemistry for the future.
I see no reason to draft a PF. We have plenty of talent at that position. I'd be fine adding a PG, SF and a C though.
As for PT with the hypothetical addition of 3 rookies:
Ulis is an ideal back up. He brings life off the bench and sets up his teammates well. His body doesn't look the type to garner huge minutes. If we drafted Smith I'd give them a 28/20 split of the PG minutes. No point in playing them together. Smith needs to learn the game and stay healthy so starting with limited minutes will help.
Booker deserves max minutes at SG (35 last year). Plenty of options to fill in the remaining minutes.
If we drafted Jackson he could get some decent minutes at SF. I'd split he and Warren's time 24/24. I'd entertain trading either Warren or Bender if we land Jackson.
Chriss looks to add to his paltry 21 m/g. He needs to be closer to 30 than 20. I'd rather see Len getting backup minutes at PF than starting minutes at C.
Again, IF we drafted Collins I'd start Chandler and try to split it 28/20 as well. Zach didn't get a lot of minutes at Gonzaga and will need to be eased into the league.
I like the idea of putting Chriss/Chandler/Warren together for a healthy mix of O/D, with the backups of Collins/Len/Jackson.