Anderson spent over 20 minutes on his back against Chael Sonnen who has had 8 of his 14 loses come by submission. I'm not saying that Anderson isnt dangerous off his back because he is, I just dont agree that he is "very dangerous".
Chael has had notoriously bad submission defense, so I don't think that it takes much for Weidman to have better sub defense than Chael. And if Chael's sub defense had been better, he would have won the first fight with Anderson (Granted that Anderson was injured and Chael was juiced up so it wouldnt have even mattered anyway lol).
"Gentlemen, we will chase perfection, and we will chase it relentlessly, knowing all the while we can never attain it. But along the way, we shall catch excellence."
— Vince Lombardi