I said the same thing to my sister yesterday. I think he has some big wins ahead of him, but he perhaps just needs to ride a little bit smarter. I know he's controversial, but trying to be objective and just judge him based on what he shows on the road, it would be good to see him take a GT stage or decent one day win.
I think part of how he is riding is (my opinion) he is still kind of in that liminal space between emerging rider and someone who can be a real threat in big races, and it's kind of the way he has to ride if he isn't yet at the point where he's getting support yet (at least he's getting into breaks and not always on donkey duty!). He was so close to winning a Tour stage already this year, in a lot of breaks and was still riding pretty strongly late in the race. Big riders for me are the ones who are still strong at the end of Monument length races and I don't think this is a fluke, being away all day and still present in the finale, nearly scoring a podium, seems like a pretty big breakthrough to me. I think he'll mature more tactically and if Lidl give him some help and more guidance I could at least see a Tour stage next season. The flip side of that of course is he may be given less rope to get in breaks but then again he is a super persistent dude, 100% not afraid to suffer, (much like Mads in a way) and will be hard to deny.
Also, ending the season on such a high note really lends itself to big motivation for next year as well; self-belief goes a very long way in such a hard sport, especially for someone who has had some mental challenges. He seems to be in a pretty good place now, going to marry his partner, etc; he'll be exciting to follow, love him or not.