Judging Nagelsmann at this stage in his carreer is not that easy I'd say. While he's already had some respectable success, he obviously still lacks silverware. But: He's just 33 years old, his carreer as a coach has simply just begun and yet he shows all the signs of someone that will become a coach of the highest level. Comparing him to the likes of Klopp, Guardiola and so forth is - just based on his age and experience as a head coach - not the wisest comparison. He's basically a toddler as a coach but still able to reach such goals.
Considering the Bundesliga is viewed as a weaker league than the premier league, I feel like his achievements on the international stage should be seen in higher regards. Assumed the Bundesliga is indeed a lot weaker than the premier league, making it out of the group stages against in a group consisting of PSG, Man Utd and Istanbul BB therefor shows top quality of the responsible coach. Even more so when you think of their last years' international campaign. It's safe to say that it's rightfully considered an overachievement for this side. Making it out of the groups and being 5 points behind Bayern domestically after losing Werner moreso shows it wasn't just a fluke last year.
If you look at their individual quality and consider that their main goal threat (who's now struggling heavily at Chelsea compared to his time in Leipzig!) shows that Nagelsmann was able to use his players properly to their strengths and elevate the overall level of his team to a higher standard than just the sum of individual quality. I think it's safe to say that this side with Werner still in it or with a goalthreat on a comparable level, they would be much stronger and not just due to the individual quality of said hypothetical player. Their players certainly are not shit, but compared to an even weakened Liverpool side, it's night and day.
All things considered I'd say that he's the greatest prospect as a coach in world football at the moment. For sure he will have huge success in the upcoming decades (!), that are yet to come for him as a 33 year old coach. While he might not be ready to manage an elite club, he certainly will be within the next 5-10 years (max). It's a lot about timing at this stage and which club will get it right once he has outgrown Leipzig. It's highly unlikely in my opinion that Nagelsmann is there to stay for more than say 2-3 years from now, he's just too good and other clubs know it. He brings everything with him that a modern coach needs, including true passion, good man management skills, tactical intelligence and the will to succeed, but also, considering his age, an open mind for changes and therefor he should be able to adapt to new influences in football easily. If Flick's time in München is over, Nagelsmann is predestined to be his successor, but that depends mostly on the timing of these clubs and coaches. When it happens, many clubs and fans mill make sad faces when they see on what they missed out.