After having 3 title challenges, getting to CL final, finishing in the top four for 5yrs, getting to x2 FA Cup Semi-Finals, x1 League Cup final, x1 Legaue Cup semi-final!! ONLY good teams do this!
Dortmund were in the relegation zone for most of Klopp's last season in Germany, he left because his methods/voice etc no longer got the desired results from the team, the same happened with Poch. This is completly understandable.
A good manager gets the best out of a squad, gets them performing better than the sum of their parts. It's why managers get sacked when they can no longer achieve this. Good managers improve teams.