No you are right. Player substitution nulls character skill. And an RPG should be about the character (the role) and his aptitude so the players are all on the same line when it comes to the characters aptitude being measured and tested. The PC might be a clumsy dimwit, even if the player would be an athlete with IQ of 170; or the PC might be the bastard child of Stephen Hawking and James Bond while the player is a uneducated mess with no limbs -- and in both cases, the game plays fairly and unbiased.