There's also a needle MLB could be threading with his tool grades, which is related to this line of thinking. Essentially, Martinez (or anyone, really) could presently have the tools to meet those particular grades, but just because he has those tools does not mean those tools translate into in-game results. So, perhaps a guy is graded with 60 power because he can put on a show in batting practice, but he doesn't have the approach/experience/etc. needed to translate that power into results when facing live pitching. Same goes for things like speed, where he might be able to run a 4.4 40 yard dash but look like a baby giraffe on the bases, or fielding, where he could have superior reflexes and instincts, but has yet to figure out things like tracking fly balls or cut-off angles for grounders.
This sort of stuff comes with coaching, experience, and time, and there's never a guarantee a guy will be able to tap into those tools to their fullest extent.