VG mentions several good points explaining scoring differences; but I'll add a few comments. In San Antonio, the PGA Tour Valero Open was played in the past on La Cantera resort course. The winning scores were normally around 22-26 under par. The Valero Open is now played at TPC San Antonio, and the winning score this year was 9 under par. I've played both courses, and there is at least 5 strokes difference in scoring average between the courses, if the wind is low. There's a bigger difference with > 15mph wind..
Let's just say, the pro's scores are much lower than mine at these courses, because as they say, "These guys are good".