Man... This comments...
Well, let's go there.
The tear that would eventually destroy all existence, was opened by the mere presence of Bill, was proven when he left his physical body and erased from memory, and the gap closed.
Other, the full power of Bill It was not shown.
Bill was hurt by a 3D robot
Yes, he was hurt, but put the cards on the table, IT WAS NOT EVEN ANGRY! BECAUSE HE IS ANGRY WITH BASICALLY ANYTHING! In addition, the eye is a small his weakness (of course it can create a shrouded eye shield, as has been shown). And he even fight with the robot with he power, and yes with his own hand.
And the weakness of Bill, is:
-Be vulnerable on the mental plane (I do not see how this weakness influence against Asriel, as Bill would not stop the fight, make a deal and get into the mind of it)
-Maned unicorn (but has been proven that this only works against PHYSICAL attacks it, that is, only against punches for example, since the laser that came out of his eye struck the Shacktron, and AGAIN, i don't see HOW ASRIEL GONNA KNOW ABOUT THIS.)
-And, finally, the magnetism of weirdness (But see that he was going to destroy it with a simple equation).
AND NONE OF SUCH 3 WEAKNESSES COULD INFLUENCE IN THIS FIGHT. So please, be smart and do not try to use these weaknesses, to the reason that Asriel would not know it.