That is Genius Uric.
In my opinion it all depends on the player.
Example: ChezDa (a replay maker) spends a lot of time making replays for videos and the entertainment of other players. He basically is used to a idle opponent, but throw him in a match with lets say Leyz; he would be at a disadvantage since his opponent is now fully capable of fighting back.
ChezDa would probably say that multiplayer is more difficult because he's not as well versed in it as he is in singleplayer.