Too many coaches don't know about pitcher arm health, or know and don't care. This coach sounds like one, if he has all the pitchers pitching every day. No MLB pitcher pitches every day. So why would a 14 to 18 year old with open growth plates pitch every day? More, at the start of the season many if not most of the kids are not in mid-season form, so why treat them as such?
As Dr. James Andrews likes to say, pitcher overuse takes many forms: too much throwing during the year without time off; too many pitches in a game; too many pitches in an inning; not enough rest between pitching outings; and, too much too soon, that is, throwing too hard in too short a time without adequate time for arm strengthening.
My son's high school team has this issue right now. All the kids throw 6 days a week, plus the pitchers throw three bullpens a week plus a few innings in a weekly scrimmage. My son says many of the kids have arm pain. I did a preseason throwing program with my son, so he's pain free so far.