You should atleast be decent at your own game, for example a game like 10 second ninja, I can't imagine the dev was the best in the world, but atleast good enough to get top 10 percentile scores. (This varies depending on how popular the game is).
You could be falling into a trap of your game being unfairly difficult, but it really depends on the type of game. For example, RTS AI at its harder difficulty is often better than most players and it is mentally challenging to beat. If you are a developer, you probably dont want to be exhausting your mental state by playing the game in the hardest possible setting, though having said that, you should still be able to beat it when you are trying hard. If it beats you frome time to time, that's well balanced difficulty.
IMO, if its to do with reactions, even if you have bad reactions, you should eventually get good at predicting enemy behaviour, after all, you should know exactly how they behave