Nantes is a low tier team. I see that if juventus can beat it easily. I will always take juventus in the match against nantes. Seeing a top club from serie a to face a low tier team like nantes makes me believe if juventus can win with so many scores against nantes. I don't wanna underrated nantes but the truth has been saying the fact if nantes was nothing compared with juventus in term of statistic of something else. Nantes will be stopped by juventus in the europa league and juventus will able to pass nantes without any problem.
I agree with your assessment (except that Juventus will definitely win - underdogs sometimes win). Now in Ligue 1 there is one top club - PSG and all the rest. Among the rest there are good teams but they are not comparable to the tops of Serie A and Juventus despite its problems are still top. But as I wrote above, underdogs sometimes win, and especially in elimination games, as it requires a little bit of luck for just two games.