Defense isn’t sticky enough year over year to use it to justify this sort of move. Just last year they were average over the 1st half of the season then came on over the last half, and they’ll probably lose Ryans this offseason.
To me their window is open as long as they have Shanahan. There’s no need to rush things, they almost made the Super Bowl last year with an awful QB. I can guarantee they aren’t giving up on Lance yet.