I think there's a Public Relations office somewhere that you can send a letter. Maybe you can even inquire if there's any other place that'd really listen to you and take what you said to heart. A lot of those theme parks are super concerned with their customers' happiness, so if enough people complain (or if one person complains loudly) you'll probably see something change.

The good thing about shirt customization is that most of it is very simple! Snipping off sleeves and collars is as easy as picking up a pair of scissors. No need to re-hem things. Trying to modify it into something more fitting would obviously require some sewing, but I'm sure it's easy enough that you can talk someone into doing it :D