What does watching a pro teach you? How to play in the odd case that your personal play style fit theirs perfectly?
You can find examples of people who aren't the brightest but just play their main game 3-4 hours a day and reach a high level of play.
If something doesn't work, you stop doing it and improve. It doesn't take the commentary of a pro to understand that. At most you'll learn nifty tricks that'll net you 2 kills once a blue moon, but otherwise watching the last 5% of a player's TF2 journey won't teach you that much. Obviously it's a good supplement but not something I'd do outside when I eat and can't play myself.