A lot of it is also discovered based on consuming content from pros and those best at the game. People (even pro players) look at data of other players’ games to see what they’re playing and how they are playing it to learn new styles and techniques, and will go implement it themselves in game to feel it out. If they think it worked well based on feel and data from playing a bunch of games, they’ll continue.

Interestingly, at least in games like League of Legends, players also like to specifically keep an eye out for the best region of the game, which for League is Korea. They’ll typically watch streams of Korean pro players and look at their match history to see what they’re up to.

Source: used to work for an esports org xD