I don't think difficult to predict the winner between AS Roma vs Brighton Albion, in this season Brighton have dropped perform in Premier League and current standings dropped until 7th place. I don't think Brighton will be favorite time for winning against AS Roma with consistency performance in domestic league after sacking Jose Mourinho and replacing by Daniele De Rossi.
AS Roma have much experienced playing in Europe League than Brighton Albion become their first appearance this season and AS Roma performed last season success lead until final round.
Playing as home match on first leg, I think AS Roma have bigger opportunity for defeating Brighton Albion exactly with their attacking line on top perform with Paulo Dybala and Romelu Lukaku had impressive performance.
Brighton performance in the English league does look unstable, but I don't think that can be a reason to underestimate Brighton in the match against Roma later, because Brighton not a club which easy to beat, especially the eropean league made main focuses from brighton for to win a trophy this season, indeed roma performance is still better in the domestic league, but at least we can see that the opponents Roma face in the domestic league are none other than teams that are considered weak compared to the teams that Brighton faces in the English league, so that's the reason why I don't consider their performance in the domestic league as a reference for guessing the winner that the match.
But on the other hand, perhaps as a team playing at home, Roma will of course get a little moral advantage from the support of the supporters, apart from that, Kaoru Mitoma injury will certainly make Roma a little relieved because it will reduce attacking aggressiveness from brighton in the match, Kaoru Mitoma is a vital player for Brighton and In fact, he is one of the most dangerous players that Brighton has at the moment.