I'm actually going to defend D&D a little bit, here. (Can't believe it, myself!)
I may be projecting/hoping, but this is the way I read LF's actions in S5:
LF was looking to become Warden of the North. He installed Sansa in Winterfell (knowing full well about Ramsay's reputation) in order to use her presence there to sway Cersei's attitude toward the Boltons. He expected Stannis and the Boltons to have a hell of a fight, leaving the victor in bad shape. Then, he would swoop in with the Knights of the Vale and take Winterfell. Cersei agreed to name him Warden of the North if he pulled it off.
What he failed to anticipate was Ramsay + 20 good men. That pretty much blew his little plan up, which I actually found refreshing. We saw Littlefinger devise a scheme, and it didn't work. He actually had to go with the flow and settle for less than he had hoped in S6.