Nothing can be done to Darius, without ruining him in SR. He's obviously balanced there, because he rapes 90% top laners, but loses lane to Kayle.
Just give us draft mode for normal games. Some heroes are just too broken in certain modes. You don't play Dominion vs Rammus and you shouldn't be forced to play TT vs Darius.
Btw, did you notice, that the most OP heroes from TT are also top tier top laners from SR? Darius, Singed, Jax, Olaf, Yorick, Rumble, sometimes Lee Sin. I'm not sure about Irelia and Shen, haven't seen them played too often. Maybe some heroes actually are too strong on all the maps?