Judy,
Understand that parents come here for advice, but do understand it is not always going to be what they want to hear.
I don't always agree with Mr. Bear, he has a way of expressing himself a little differently that us moms may like, but IMO, his advice was pretty much accurate as to what you should or should not do.
BTW, IMO, if this was a good pitching instructor he would be instructing your son to long toss, as this does strengthen arm, as Bum has suggested to you, your son as a lefty has to throw harder, lefties that don't throw hard tend to use their off speed for success and never develop their FB, which is always the most important pitch to develop.
We tend to see things as parents differently when it is our own, but at 16 your son shouldn't be coached by you as to what to say to the coach, in fact if he really wants to make a statement, improve in the game and that speaks louder than any words. It may take a whole season, but he has senior summer and all of next fall and then more to improve to where a college coach will take notice. If son had to rely on HS ball he would be doing something else right now.
Learn and listen from the folks who have been down the road and accept and embrace that we do understand your dilemma, but we can't hold our players hands forever, they need to figure it out for themselves, and you know what, they do!