It's still too early to say that, Liverpool is indeed a very strong team this season but what you have to remember is that this is the Europa League where surprises often occur every season, so I think it's not a certain thing for Liverpool even though they are the favourites.
In Europa League, you can’t tell who are the most preferable to win the league yet when they’re just in the group stage of the competition. Teams are coming from champions league to join them after the group stage, and some of them that come from champions league are usually big teams which aren’t lucky to get a qualification to the knockout stage of the champion league. When they join the Europa League, their performance their will now be used to quantify the overwhole teams and the one that will likely win the Europa League.
And Roma also cannot be underestimated, they were finalists last year, although now their performance in the domestic league is inconsistent, but look at the quality of the Roma team, there has been an improvement and as long as Jose Mourinho is their coach, I think they should not be underestimated.
With Jose Mourinho been the manager of Roma, I still have a very big hope in them that they can also be a potential Europa League winner this season. Rating a team by their domestic league performance is not always the case now, they play differently in different leagues, so they have an advantage still in the Europa League title contenders this seasons amongst others.