If you aren't specifically training and eating to get big, you aren't going to get big. Dan John says putting on lean muscle is the HARDEST training goal there is (I think he put it over fat loss). I think just looking at the strength/flexibility accomplishments of many StrongFirst instructors (for starters: Pavel himself) should help relieve fears of strength necessitating tightness. Don't stop training flexibility. Also, in Easy Strength, Dan John does say there is a point where stronger doesn't necessarily mean better. For most power sports, he puts that at 2.5xBW DL, 2xbw back squat, 1.5xbw bench press. If you have those and aren't excelling at your sport, more time in the weight room is NOT going to get you any farther. And he's talking about contact sports where size and strength are a premium (eg, American football).
Also, there are plenty of sports where a coach may be concerned with an athlete getting too big. Any weigh-in sports, obviously, if you aren't training to compete at the next weight class. Also, I've seen players losing weight to get better in basketball, hockey, and football, and not all from fat. There does come a point where size is a hindrance to agile athleticism. It's physics.