im not saying that FPSes arent isnt hard for everybody, im comparing the genres
give a person a who has never played videogames counterstrike vs easy ai or dota vs easy ai and you know which one they will struggle with more.
i agree that character control is something that must be learnt, but thats something that exists in mobas in addition to all the other knwledge required
we can create straw men all day but to counter your tic tac toe example, here is some rock paper scissors tournament
http://www.airguitaraustralia.com/RPS index.html
http://en.wikipedia.org/wiki/Rock-paper-scissors#Tournaments
how about a more gamey example - tetris - four controls that are quickly learnt (rotate, down, leftright, hold) and one rule - clear lines. There are tournaments for that too. Esports dont have to be complicated. Gamers just prefer that they are.
people will compete in anything theres interest for, whether or not your game is fundamentally complicated