ARC is intended to correct the deficiencies in the room (while you are mixing). If your room is boomy then with ARC off, which yes you turn off for export, the will sound boomy. But remember that is your room your hearing (with ARC off).
So the real test is to take your mix to other environments and see how the mix translates. If for example your mixes sound better in the car (assuing you don't the rappers delight sound system in your car) than before you mixes with ARC you can be sure ARC helped you to make a better mix.
In my room which is pretty boomy, ARC definitely helps to control that boominess whale listening through the speakers.
I'm sure you know thi but NEVER listen with your headphones thru ARC. It will sound so wrong.
HTH.