Erik Ten Hag had a bad time in Manchester United but was successful in Ajax, where he led the club to win three Eredivisie titles and reached the Champions League semi-finals. There are reports that his performance alone in Bayer Leverkusen was not the reason why he was sacked. He fell out with the club management regarding player signings and the future direction of the club.
The club management shouldn't have expected immediate position results after they sold Florian Wirtz, Piero Hincapie, Jeremie Frimpong, and Granit Xhaka, and Jonathan Tah without worthy replacements. He should have been given some time to build the club. Some successful coaches were given more than one season to get it right in their clubs.
That's because Ajax cannot be compared to Manchester United. If the problem really is player recruitment, then it makes sense because Ten Hag intends to recruit players who have played for Ajax, as he did when he was Manchester United coach. Leverkusen on the other hand made a mistake by hiring Ten Hag, but firing him early on was also the right decision before the league progressed further. The results from the two matches he managed provide evidence that Leverkusen is regressing rather than progressing.