In Preston Sturges' 1940 comedy "Christmas in July," an office clerk dreams of winning a fortune by winning the grand prize in a contest to name the new slogan for "Maxford House Coffee." His entry? If you can't sleep at night, it isn't the coffee - it's the bunk! He spends the rest of the movie saying, "Get it?" They do get it. They don't like it, but they get it.
Spring training battles are the bunk. The Yankees catching battle in spring training is a great example. If Francisco Cervelli and Chris Stewart play as much as they can, they might max out at 50 plate appearances each. Against that, you have 148 games and 394 plate appearances for Stewart in the regular season, 184 and 562 games and plate appearances, respectively, for Cervelli. Both are of an age where they're not likely to suddenly manifest new abilities, and while I suppose there is an argument to be made that both could show more consistency with regular playing time, that's not necessarily something you're going to see demonstrated in the spring, when playing time is by necessity sporadic.
The whole exercise then is somewhat farcical, because the observer is unlikely to get enough information to overturn what he already knows about a player. More typical rookie-veteran spring training battles are even worse. You know what your prospect did in 500 Triple-A plate appearances last year. You know what your veteran has done in 5000 major-league plate appearances over the last ten years. What either of them does in 50 spring training appearances in windblown stadia, some of them against the other team's 17th-best pitcher and with half their Double-A defense in the field, shouldn't be weighted more heavily than what you saw in the previous 150 games from the kid, or the previous 1500 from the veteran.
What makes these affairs even more pointless is that humans suffer from a recency bias, the tendency to conclude that the current trend or pattern will continue. If you watch three games and Player A goes 0-for-9 and Player B goes 5-for-9, you're going to instinctively rate Player B as the hot hand worth playing, even if Player A is Joe DiMaggio. Spring training hitting may tell us who is hot in spring training, but it doesn't tell us who is the better hitter overall. You need more time and stricter conditions for that.