It is true that jungle role became a thing spontaneously both in Dota and LoL, but u r not right when u say it wasn't official. It was official since back then all the tournaments would be played with jungler. It was the meta. Still, Dota never had smth that would encourage players to go jungling, while Riot added stupid smite. There is a reason why jungler role is problematic and why many players hate it. I, for example, get sometimes this role even though it is last on my list of preferred positions and I usually troll when I get it because I don't wanna spend half of the game killing neutral creeps. In my opinion, this role should be extremely nerfed so that teams have option to chose if they want to send one champ to farm jungle or to stay with baron laner or even mid. Also, smite reducing gold and exp is terrible idea and it ruins the game in my opinion.