To be fair to Munch, a TON of experts project Sale's delivery to cause arm problems. This is not just ESPN. Heck, our own scouts were torn on his best role and our president and manager thought he should be a closer. It is not a non issue. That said, it also is not a major issue until injuries do pop up. It is just something to monitor, not ignore.
That said, A knuckle curve would not be a good pitch for Sale's arm angle. I threw one in college and still break it off in my men's league know and then, and it is tough to throw from the side because you really have to get on top of it and spike it. Sale's breaking ball is perfect for his arm angle, that slider is one of the 10 best pitches in baseball. His changeup has a TON of potential and might ultimately be his best pitch.
For Sale, he is doing what he has to do. He got to where he is by being a thrower, just over powering guys. If he wants to be an SP, he has to learn to pitch. Know how to get outs by dialing down his velocity, placing the changeup and making the slider disappear. Sometimes, you just have to hope a guy holds up. I am sure plenty of scouts today would spazz out and try and make Randy Johnson a closer as well.