Topping meters in LFR tells nothing to you, most players there are not even trying.
Topping meters in Normal just tells that other players in your raid are either less geared than you or bad players, it is that simple, you can check from raidbots, world of logs and simulations (you might say that these are not always right, but they are if you are using them the right way, not looking at cheesed logs etc. especially in this case the difference is really big) that Arms IS underpowered in PvE, that is a fact, so your opinion doesn't really matter..