I once had a player tell me "out of character, it's obvious where this is going." I was just making it up as I went. I think she's the only person who knew where it was going.
Last big fight was all the previous undefeated enemies in one place. Players gave me an excuse to ensure they all met up so I took it. No more 5 loose threads: just one huge fight.
It takes a bit of time to adjust your thinking, but it's actually easier to prep scenes instead of plots once you get the hang of it. You were preparing them in the middle of your plots anyway, so it's not like it's more work than before.
The hardest part is resisting the urge to prepare a monologue you know will likely never happen in-game.