Actually, his performance case this season has been improved more than that of last season, Dembele scoring most of the goals for PSG this season is incredible and currently the overall highest goal scorer in the league.
I never see him to that level of getting nominated for the Ballon d'Or, there are quite other players across Europe that has done incredibly well more than Dembele, individually both for club and for country's side.
If he wins the Champions League, it could be an exception because maybe he will be included as one of the candidates for the Ballon d'Or. Dembele has developed quite a lot this season and he has fully contributed to the team, this is different from the previous few seasons where Dembele lost his best touch when given the opportunity by the coach. There are many players who have achieved the best careers with their clubs so the potential to be included as one of the Ballon d'Or winners is quite open.
Dembele has indeed made some progress this season, but I am not so sure he will be included as one of the candidates for the Ballon d'Or if he fails to bring PSG to the Champions League final because there are many competitors who might be his strong rivals.