He has actually proven himself to be an excellent manager. Just look at his stats since he became Dusseldorf manager. He took charge of Dusseldorf midway through the season at the start of February 2022, when Dusseldorf were in 16th position in the league. Thioune then went undefeated in his first 12 consecutive matches as manager of Dusseldorf. Fortuna Dusseldorf would finish that season in 10th position, well away from the relegation zone.
In the 2022/23 season, which was Thioune's first full season as manager of Dusseldorf, Thioune managed to get Dusseldorf to finish in 4th place in the 2 Bundesliga at the end of the season. Then the following season(last season), Thioune managed to steer Dusseldorf into finishing the 2 Bundesliga in 3rd position in the league table. This season so far, Dusseldorf are top of the league in 1st position. It's obviously early days yet, but it just seems like he is improving this Dusseldorf side season upon season.
In today's match, Thioune's decision to bring on Niemiec as a substitute when Dusseldorf were trailing to Koln, proved crucial, as Niemiec would score the equaliser that earned Dusseldorf an important point and the 2-2 draw. It's been an excellent start to the season for Dusseldorf, where they have won 4 matches and drawn their other 2 league games. With Thioune at the helm, one can't help but feel very confident about Dusseldorf's chances of getting promoted this season.