It's hard to say the Spurs need to shift paradigms when they are only not "championship contenders" because they might not be able to beat the Warriors. That's only a temporary obstacle. They would beat Houston and OKC in the playoffs, so it's not particularly clear that those teams have the right paradigm either.
The Spurs' weakness in their back court has nothing to do with Pop's philosophy for roster management. It has everything to do with the individual players declining. These guys in their 2014 forms would form an elite perimeter unit. The reason why that seems like a style other teams don't follow is that other teams don't have four backcourt guys who have been good enough and selfless enough financially to stay together that long. If the Warriors stay good for three or four more years, we'll stay to see them go the same way. Utah let their guys play forever. Nash and Hill were there until they were jerky. Memphis only let Carter and ZBo walk because they switched coaches, and they are clinging to Marc and Conley even still. Dallas with Dirk and Barea. We can keep going.
Mills isn't old, used to be dynamic and was important for chemistry. I wouldn't have kept him, but I don't think it was a bad move, especially independent from salary. Manu was iffy, but he's playing so well that isn't the problem. Parker played well to end his season last year and may still do so again. I've wanted them to upgrade the backcourt for years now, but I also think they are playing about as badly as they are going to play this year. The team drafted two guards in a row along with having a promising one in Forbes locked into an Arenas RFA situation. It's not like they don't have a semblance of a future there. The plan going forward is to get the most of out Parker/Murray, keep Manu on ice, get Green healthy and hope Patty can become more consistent. That's dicey, but it's not that much worse than hoping Gay and Kawhi are healthy, that Pau stays effective in May and that Anderson or Bertans can be a rotation player going forward.