You said it was a losing "factor" without specifying how different factors weigh against eachother.
Am I to understand if I take a Fief, as a losing factor it would outweigh ALL winning factors until some time condition is met?
The time condition aspect would still seem to me harder in the early game, easier in the late game. And it would basically just involve people waiting around on defense to meet the specific time condition to make peace, which I'd consider to be equally gamey as paying for peace is while adding tedium. I just don't see how it fixes late game challenge, it just adds more grind between fief taking.
Take fief, turtle for X time, propose peace vs. take fief, propose peace. The turtling aspect is more to do, but if you're in the late game it's not more difficult in terms of strategic challenge - overall I think it would only accomplish a delay in map painting.