It's an old post, hopefully you get this, I have a moonroof deflector. I haven't driven without it, but my veh is quiet when I drive, it would be more quiet if the screw for the moon roof hadn't broken on the driver side.
I don’t have a wind deflector on my Forester but in my previous car, Mazda 3, it had one and one day I took it off to try without it and it was really loud without it. I used the moonroof year round (100F through -7F) the only reason I’d close it was rain. The only issue I had with the deflector was when going through a car wash sometimes the rinse cycle wouldn’t get rid of the soap underneath the wind deflector.