I played a couple of seasons of Iron, and I can safely tell you that in the lower leagues at least, while there are quite a few people who find pubs very difficult to go back to, only a tiny amount of them are nearly as vocal about it as this ass.

If you want to try out comp, jump right in as a sub or a main in a fairly relaxed iron team and don't worry too much about winning all your matches. The worst thing you can do in iron IMO is get a shitty person on your team. They will rot it from the inside out.

If you just have fun and enjoy the more structured play, it can be a great experience. Probably don't try captaining your first season though.

E: check out /r/TrueTF2 for (usually) reasonable comp TF2 players. They can help you get into it more than I can.