Indeed I won't doubt that mourinho and Roma have all the chances to reach the final but reaching the final is not the only issue here as they would need to win the actual finals to be call champions and the other semi finals has a feature of teams that is well experience and exposed to European football.
It is harder to win semi finals in aggregated result than to win only a single match like a final match. You will no longer to worry about anything after a final match and can spend all resources you have for that match.
Champions League final and Europa League final usually are last matches in Europe and the times those matches often are hosted will give participating clubs more concentration for those matches. Usually domestic leagues finish before those finals and in some nations, only their national cup final matches will be hosted after final matches in European Leagues.
I think Roma will have big challenge from Leverkusen but they can beat Leverkusen with many conditions, they play well, be able to score goals, defend good enough to block Leverkusen attacking and prevent the opponent to have goals.
Juventus and sevilla are two strong teams that have been doing well especially sevilla, I think like Madrid are called king of the champion league same goes for this excellent sevilla team in the Europa league.
I consider Sevilla very high but I hope to see Juventus will make an Italian final match in Europa League with AS Roma.