First of all, I don't think anyone needs to have played the game (or been a decent athlete) to understand the concept of high pressure moments. In fact, I could argue those who play the game have their opinion swayed by their own experiences. "Pressure" itself becomes a subjective concept.
No one ever denied certain hit and moments are "clutch." But what we frequently forget is, especially in baseball, there is always more than one person involved. Back to Mueller, was his hit really "clutch" or was that a choke moment for Mariano Rivera? And while no one likes to think of Rivera as anything but a post-season fountain of ice water (despite his being the only pitcher in MLB history to lose the lead and game in the ninth inning of game 7 of the World Series), so he couldn't have choked? Right?
But what about Dave Henderson? Again, a massive clutch moment. But was Henderson clutch or did Donnie Moore choke? How do you draw that line? If you believe Moore choked, it certainly has to somewhat refute the argument that Henderson was able to "step up his game" in a high pressure moment...