It was the same at Leeds after Revie left, albeit they should have won the European Cup within a year of his departure under Jimmy Adamson.
Fword also after Clough. Newcastle after Keegan.
When you've had somebody bigger than the club who eclipses its' history it seems to take well over a decade to get over the loss.
Liverpool might have suffered similarly had they replaced Shankly with an outsider instead of the continuity.