That feat over Shanks could be because of him already having df or his haki. Things aren't sure about this.
And, yes he needs mastery over df lol
He pulled something basic at MF that doesn't mean he doesn't need mastery over df especially to have gura awakening which takes time.
So, as time passed since TS, his stats definitely improved because thats just basic shonen logic for a future antagonist who was running parallel to MC in covering grounds to get the throne