ARod says he didn't get caught, the MLB says he did. You can choose one side or the other but the arbitrator clearly felt it was enough to suspend ARod. If there was literally no evidence against ARod or proof that he didn't take PEDs the suspension wouldn't have stuck. The fact of the matter is ARod cheated, got caught and now has to deal with the consequences.
It is ridiculous that a suspended player's salary doesn't count towards the luxury tax though. If teams were punished for steroid use instead of the players we would see PED use plummet but, that is never going to happen.