I agree and maybe if someone was in that situation now I'd like to think they'd be given a chance to try.It just bothers me when a young person is told that he/she can't do something. That is the time in life when one should be able to try, at least.
Good thing they didn't ask you to play a flute. It took me 3 weeks to get a note out of my flute first time I tried. Clarinet I was good to go luckily. So much guesswork as you say when you have never played one.At school we were offered extra music lessons in either the clarinet or brass. We had one go with the main music teacher to get a note out of a clarinet - literally no instruction, just guess, and blow one note.
if you couldn't do it, bad luck if you wanted to learn the clarinet, because they sent you off to learn brass instead ( no try out for that), which is why I spent 5 years playing the euphonium