My son was a position player for the 1st 3 years in HS. His senior year was asked to do some pitching also due to a couple of injuries. His last two years at JC he also wa a two way. Several issues come up for the two way, expecially if he is a starting pitcher.
1) Arm recovery. Throwing 7 or 8 (JC) innings then coming back 2 days later and throwing from 3rd base or the outfield. Arm is still not full strength.
2) Bullpen time conflicts with fielding or hitting, unless you come early or stay late.
3) Hitting, along with practice, I haven't checked, but my guess is his batting average on the days he pitches is not the same as the days he doesn't.
I do agree with the above, if you can, play as many positions for as long as you can. Play where the coach wants you.