Most of the veteran bench players were regulars at one point in their careers, which can make it easier to adjust to just being a bench player. A lot of times composure and preparation are keys when it comes to being effective as a pinch-hitter. Rookies and younger players will likely struggle with this greatly. Most rookies were regulars at one point in their professional careers as well. As baseball fans, we are just conditioned to believe that the sport they play in the majors is somehow intrinsically different than the one they play in the minors. Really, everything you wrote above is what we hear from announcers and managers ad nauseam but I've never seem any clear evidence that it's true. That's really what this whole thread is about. There are good and bad, young and old bench players. At least with young bench players, they have the chance to improve and surprise. If you are an old bench player, it just means that you've already proven that you aren't good enough to start. While it wouldn't surprise me if veterans perform slightly better than rookies of comparable talent in a bench role, I've never seen any actual evidence that it's true. Just dogma.