Twisted fate is just a good ganker due to Anywhere teleport. Sejuani is fine where she is, if you know how to play her. She's about that crowd control, IF you were to give her a speed boost, it should be on her W.
Edit: I guess that would kinda make her like Shyvanna though. Either way, I still think Sejjy is fine, She has good initiation, tackle to halt enemy action for a split second, good powerful slow, and that Ult. So unf. People just forget tanks aren't supposed to get the kills. Although without heart of gold, I feel as if she'd fall behind fast. GP10 Crit sword just wouldn't help her as much........ But.......... Mreh.