The whole "provably fair" only proves % going in and out it doesn't mean their own plants aren't the only ones winning.
I don't think you understand provable fairness. It doesn't tell you anything about the overall house performance. All it tells you is that your own bet was fairly processed. That's pretty much the opposite of what you claim.
Look at bitzino.com. I have no idea how much they've taken in bets, or how much they've paid out. They don't (to my knowledge) publish that information. But when I play there, whether I win or lose, I am sure that the bet was handled fairly due to the way that all their games are provably fair.
I have to read up some more on it but from what I understand since the seed is created server side and since most dice sites use "investors" the players betting may be "provably fair" but an insider is still able to cheat so it won't be fair for all.