Sure there are those occasions, but you also have to balance that with the fact he had Tom taking points off him every weekI would counter that with Dally Ms being extremely flawed. If judges watch a game and noone stands out, they will give it to a big name player.
It also favours highlights, so you could go missing in an unspectacular fashion for 79 minutes and slot a field goal to win the match, then you get Dally M points even if you not doing your job contributed to the opposition still being in the game in the last minute.