Disagree.
Spurs have struggled at the backup PG spot for years but you try to explain that by a wild theory (Pop being a good coach except for backup PG spot

) while in fact the explanation is as simple as it can be.
The last time Spurs had a good backup PG was in 03 with Speedy. Since that, Spurs never spend more than $1.5M per year on a backup PG. The less money you spend, the harder it is to find a good player. Spurs never made the investment to get a good backup PG. You can regret it but when you had a limited amount of money, you had to make choices.