Ehh. I saw the build on spectator, and those are supposed to be high-level games. He was doing really well.
1. Do you have the same runes?
2. Are you able to replay that same style, even with the random criticals and random Q bonus damage involved?
3. Could you do the same thing on the opposite side of the map?
4. Did he ever get counter jungled? By who?
5. Would the result be the same if he was counter jungled by another champion?
6. Does it completely depend on who he's up against? (the whole team, not just the jungler)
7. Does it also completely depend on who's on his team?
You have to understand that some people will pick a champ based on something very situational. You can't just pick jungle Yi every game and expect that same result. If you want to learn jungle, you're going to have to play multiple jungle champions. Not just one. If you plan on doing ranked or tourneys and you want to be able to pull that off, you'll also have to start practicing draft, and unlock every champion.
You will have to know how to pick according to bans and who on both teams pick what champion. You'll have to be able to co-ordinate with your team. You may even have to pick someone else's champion for them in order to trade after, which is why you'll need all of them. If you ever have to drop out of champ select because of what the enemy team picks or bans, then you're not a good player. If you pick the same role or same champion for that role all the time, then you're not as useful.
Champion select is a hard part of the game. You've got to think carefully.
Also... Never. Lock. In.
It does nothing good. Nothing.
Edit: 
Final words. These are my thoughts to ANYONE who says a champion is a for sure pick and will always work just because tournament players can do good with them.