The reason you see shotos online is because people are more used to them so they pick them. Ryu/Akuma/Sagat are probably the top 3 but outside of that the other shotos either are mid-tier or lower. I think some people pick Sagat because he's easier to play and somewhat overpowered, but the reason you see so many Kens and Ryus are probably more to do with them being iconic to the Street Fighter series and people generally liking them more than the other characters. Capcom can make Ryu and Ken the worst characters in the game but it's likely people will still play them because they still like Ryu and Ken. Zoning and fireballs are a huge part of Street Fighter IV so if you don't enjoy that aspect this really just may not be the game for you.
I couldn't find anybody I liked to play as in IV so I quit playing after a month. I'm getting Super since I know I'll enjoy playing as Deejay but well he's awesome so yeah.
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