None of your managers took a team languishing at 17th and brought them to top 4 within a season. And none of your managers took a club that was founded 11 years ago into the semi finals of the Champions League within 1 year. Hasenhüttl did an ace job, but that doesn't really take anything away from the fact that Nagelsmann has done brilliantly too. Sure he's a work in progress, but he's quite obviously a top manager in my eyes (top manager being subjective in definition it appears. You look at it as winning something, whereas I don't solely rely on that if a manager hasn't been equipped to be expected to do this). Top clubs are already after him, and his achievements are fecking impressive.
When Nagelsmann took over Hoffenheim and helped them survive, they only won half or 7 of 14 matches to survive by a point (37 total points). There were 4 teams within 3 points of the relegation zone. His first full season was very good as everyone agrees with 25 points increase (62 points) and qualified for the CL qualification round. His final year at Hoffenheim, they finished 3rd in the league, but with 55 points. So Hoffenheim finished with 7 points less in his third and final season, but then finished a spot higher than the previous year. And in CL, Hoffenheim finished last in the group (City, Lyon, Shaktar, Hoffenheim) with 3 points, from 3 draws.
Again, RB Leipzig finished in 3rd position with 66 points in the Bundelsiga in 18/19. In Nagelsmann's first year with Leipzig and with a better team than last year, RBL finished 3rd on 66 points. Their goal difference in 19/20 was +10 compared to the previous season, but final points total and league position was the same. The CL run has been very nice, but it's only one season and has to follow up with similar results at least for another year or two before his stock increases further.
He's a young and innovative/bright manager, but he still has loads to learn and show that he can be consistent with expectations and better results. If RBL can continue to improve and push for 2nd spot or maybe even the title in Germany within the next few years, then that'd be a tremendous growth path for Nagelsmann. He might not even get the chance to see that through because he could be picked off by another club within that same timeframe.