The competition during the regular season had teams of varying strengths, and in certain games, the Argentinean's performance as a starter was indeed impressive. This overall outstanding performance led Popovich to live in an illusion he had created, believing that Manu Ginobili was an excellent starter.
However, the consecutive poor performance against the Warriors proved that in high-level matchups, Manu Ginobili was not an exceptional starter.
In fact, Popovich had already discovered this issue in the original timeline during the 2005 Finals: "Manu plays too fiercely and actively, while an average player would tire after 8 to 9 minutes, his game intensity would exhaust him within 6 minutes. That's why I considered having him play as a substitute, to completely destroy the opponent with his rhythm."
Now, Roger had let him realize his lineup shortcomings in advance. Maybe this could save Popovich in future games, but tonight, they were already powerless.