this. guys make it to the big leagues based on hitting. There literally thousands of guys who can field as well as a lot major leaguers but can't hit their way out of a batting cage. The flip side of that is that once that ultra-selective hitting filter is applied, a lot of guys that are left just are not natural, fluid guys with the glove. When you have one, absolutely develop him as far as you can, but when you have a guy for whom every ground ball is going to be an adventure (Casty), I agree the best thing you can do is let him percolate at one spot and get as good as he can.