Yeah, that's why this talk of a Murray-White-DeRozan starting perimeter trio next season and probably beyond, is insane and it'll only be exacerbated if they're going to try to shoehorn Poeltl into the starting lineup as much as they can.
The only way to attempt to make sense of this roster going forward, is if Forbes is traded and a starting caliber wing is acquired. Otherwise, the 5th/6th best guard/wing on the team will probably have to continue to start, which would mean rotational gymnastics would be required for him to receive the minutes commensurate with his standing, as well as the others with theirs.
Well if you look at shooting percentages, White shoots as good or better than Tony Parker did, from every range - except 3P, where he shoots much better. You might not know it, but he's shot .538 on corner 3's. White's biggest problem is shooting unassisted straight-away 3's. I'm not trying to compare the two as overall players. Just saying that White's shooting is adequate for the job and I think he's just getting started.
Murray, on the other hand, needs to get all the way to the hole before he can score effectively. BUT... by the second half of the season he was much improved. His TS% in the playoffs was actually pretty good. (He's aggressive going to the rim, and draws a lot of fouls.) Yes, his shooting needs to improve. But between his defense and rebounding, he secures a lot of possessions for the Spurs. It will be interesting to see if he comes back shooting like the second half of last season, or the first. I said it in another thread, but I think he will benefit a lot from not having to pretend to be a PG.