I think having these cards right next to each other explains it quite well.

while the idea of Ugin into Titan woul make sense, the reality is "ugin, 0, rock, rock, rock. Oh look their board is wiped"
(But Karn Liberated is a solid walker and usually scales well with power level, that would be my vote if you're looking for a colorless "Titan planeswalker" as a control win-con.)