My son is in a similar position, trying to keep it going as a hitter/corner infielder and pitching as well. He has heard it from 90% of the coaches and other judges of talent that he will most likely have his best shot as a pitcher. He is 17, 6'4" and a solid 205 lbs; throws hard some days (clocked at 90 two weeks ago) and not so hard on others. Just a week or 10 days after touching 90, he barely hit 80 at a scout team tryout with college coaches and their radar guns in attendance. He had spent about 7 hours taking swings, ground balls at first, and standing around in 90 degree weather before taking the mound, but so had most of the other kids who got on the hill.
He has worked hard on all parts of his game, and especially his hitting. He works more on his hitting than any other part of his game, but also takes hundreds of ground balls every other day, lifts weights, and plays tennis for conditioning. However, he has not spent much time working on the boring grunt work necessary to become a good pitcher. He hasn't played enough hard catch, religiously, to develop the stamina needed to go out and throw 7 innings without his arm hurting for 3-4 days afterwards. He has plenty of resources, reference books, and has worked with 3-4 different pitching coaches, all of them good. He still hasn't approached pitching real seriously, despite the fact that he is a smart kid and knows better.
Besides playing this fall for a scout team in Southern Calif., he is also playing on Saturdays for his HS fall ball team. Today they played three games, and by game 3 the team had run out of pitchers. He had thrown yesterday (3 innings), and yesterday was one of his "on" days. He was excited about how hard he had thrown, and his arm felt okay when he went to bed last night. Today he was at shortstop, and by game 3 was obviously hurting, struggling to get the ball on a line to first base. He didn't let on, and the fall ball coach didn't notice or didn't care and asked him to close the last game with two innings. He went out and tried to throw through the discomfort, and somehow got through the innings, but the lack of conditioning was obvious. It is hard enough to throw back to back days when your arm is in shape, but trying to do too much in the field, at the plate, and on the mound is going to lead to injury. All those ground balls and practice swings aren't going to help him if his arm falls off.