Very true. Nagalsmann was very much the toast of the Bundasliga which helped him though. I feel like managing in Portugal won't get you recognized as much.
He's won the league with Sporting and at the very least made it into the knockout round at Dortmund's expense. Every club in Europe knows his name already.
The question is whether they like his approach and think he can make the switch to another country/language. I doubt one game against City, which they were always supposed to lose, will make any real difference.