He never was in LCS though, only CS
To play Yi you only need to know your timings for Q & W for aa reset... rest of champ is ezpz
Yasuo requires way more than Yi, but not close to Riven at all.
And to play Riven on the highest level... well there are only a few people who can pull that off (viper, Adrian for example).
Biggest problem with Yasuo/Riven players is that they are impatience and therefore quickly make mistakes because they are bored... and then they end up 0-5