I almost wonder if Hannibal sent Will to Tobias in the hopes that Will would kill him.
I think Hannibal wants Will killing people.
I think he called Hobbs to set up an emotionally violent scene that would most likely end in someone’s death. Will ends up killing Hobbs and it shatters his mental state.
Will comes to Hannibal and confesses to hearing things.
Hannibal then suggests that Will run off and talk to a reckless serial killer.
He knew Tobias would attack and he was hoping Will would kill him so that, 1) Hannibal didn’t have to worry about Tobias and 2) Will would be forced to end another life and further crumble his stability.
Hannibal doesn’t want to help Will, he wants Will’s problems to get worse. He wants to groom Will into his perfect friend; to do that, he has to break Will first.
I do think it was harder for Hannibal to knowingly send Will into danger that time. But, he did it because it’s what he has to do if he wants a true friend.