3.5 million when Blackout was released is rather poor... BEYONCE's 3 million is not something to be at all ashamed of in 2013-2014. Y'all can't just compare album sales like that.
That being said, I love Blackout more than BEYONCE, and I feel like Blackout is under appreciated critically and commercially (it just hit platinum a couple of years ago). BEYONCE is her best album, a title it shares with B'Day and Sasha Fiercw imho, but it's not the 2nd Coming. That's not to say it wasn't revolutionary and had crazy impact, because it was and it did.
So, yeah, I say BEYONCE is more overrated.