I think that Sevilla is no weaker anymore than Juventus. This is not because Juventus wouldn't be better on paper, I think they are still better on paper. But now is a situation where Sevilla exactly knows how to stay in the competition. It is similar to Real Madrid who played a below average La Liga season, yet they are among the top favorites for the Champions League because they have proven too often that they can show a different face if needed. I think Manchester City is a slight favorite, but still Real Madrid has as much of a chance to beat Manchester City as Sevilla has to beat Juventus.
To be sure, bookies favor Juventus in the first leg. although it is not a real benchmark, it shows that Juventus has a higher probability than Sevilla in the first leg. after all, lately Juventus have started to experience a little change in terms of performance, they won matches in their two matches in the domestic league. although it doesn't determine anything in the match later, Juventus have the advantage of playing at the Allianz Stadium, their own headquarters. After all, Allegri knows that the opposing team cannot be underestimated. but with players who have more quality than Sevilla, they will give a fierce battle to win the match.
On the contrary, Sevilla was well aware. that in the match later, it is not certain that luck will be back on their side. so, at least, the Sevilla coach will prepare his team for the match later.
by the way, in the first leg, if the odds are ideal I will bet on Juventus.