Carter hit .294/.358/.465 for Triple-A Pawtucket in the International League last year while the property of the Red Sox. Decent numbers on the surface. However, putting up those numbers as a 26-year-old in Triple-A is a far cry from doing so in the major leagues.
According to the Minor League Equivalency Calculator, Carter would have batted only .247/.300/.382 last season in the majors, with only 12 home runs and more than two strikeouts for every walk. Defensively, he is known as a poor first baseman. You can sugar coat it all you like, but these are bad numbers.
Equivalencies (known as MLE's) are not the be-all-end-all of prospect analysis. In fact, great players will often elevate their game as they progress and beat their MLE's easily. Just one example is David Wright in his rookie season in 2004. Wright posted good stats in Triple-A, and then, although he took a step back in the majors, he posted numbers better than his MLE would have indicated.
But for most players, MLE's provide a good quick glimpse at what they can be expected to produce based on what they have done in the minor leagues. As another example, if Fernando Martinez were in the major leagues last year instead of Triple-A, his MLE was .245/.280/.438. He had rough discipline last year but slugged the ball like crazy, and that showed in his MLE. The big difference between Fernando and Carter, however, is that Fernando is a rapidly improving youngster while Carter is already 27.
All of this is to say that Carter's spring performance, although great, is likely to be a mirage. Certainly, the Mets have to take into account his 2779 minor league at bats when deciding whether he is a better option at first base than Daniel Murphy -- and to weigh them much more than 30 great at bats in spring training.
From my view, Murphy should get the job barring a complete collapse at the plate. Murphy was an excellent defender last year and there is no reason to think that his improvement in the second half last year wasn't real. His minor league track record is solid and in line with what he has produced so far.
Carter might not be getting the consideration that many Mets fans feel he deserves, but that is because he is probably not the best man for the job.
In fact, we looked at Murphy a couple of weeks ago here and concluded:
How did Murphy fare in the second half of the year, when he said he felt comfortable with his adjustments?
Pre All-Star: 25 bb, 30 k, .248/.314/.364
Post All-Star: 13 bb, 39 k, .282/.313/.485
September: 3 bb, 10 k, .290/.308/.580
* * *
If his improvement [in the second half] is legitimate, and he gets a little more luck this year, and if he has a capable right handed hitter batting behind him (so that lefties can't eat him up), I think he has a chance to hit .280/.345/.480 this year with 17-20 home runs.