I did feel exactly the same way you would have, but what are you going to do when your son tells you he had a "blast" and he actually means it?
I could have said something to the coaches, but determined that that would be counter productive in every way. And who knows, maybe had he played he would have cost them the game and then all the fun would have disappeared. Somehow everything worked out well in the end.
Very similar story for me (well, without the kid going to MLB! At least as far as I know!). When 2019Son was starting up his 12U year in September he joined an "elite" team (not trying to define that in this thread! Let's just say a competitive Majors team in SoCal). He had previously played a total of two travel ball tournaments in his life -- one in May and one in July. He was, essentially, a rec ball player. In September the new team had a big tournament in Vegas -- I took a Friday off work, drove to Vegas, paid for the tournament, hotel, etc., and he got 3 ABs the entire tournament and barely played in the field (as I recall, there were only 12 kids, so everybody played a lot, except for 2019Son). I kept my mouth shut. 2019Son wanted to quit the team, but we have a family rule that if you join a team you have to see the season through -- in this case, he had to play through the end of the year. He ended up playing 12U and 13U for that team.