Porto have a better record for head to head against Roma, Roma have recorded two wins, two draws and a defeat to Roma. The home side has shown resilience in their recent fixtures and have proven to be a stronger side playing at home with a good home record compared to Roma's away performances. I predict Porto to get a win against Roma in their Europa League meeting.
What you said is possible for Porto, but Roma could make a surprising change in the match so they can give their best at their opponent's home. Actually I am not completely sure about Roma winning at Porto's home, but in the Europa League there are always unexpected surprises and Roma could make one in that match even though Roma's condition has not been so good lately. But that doesn't mean Roma can't bounce back in the upcoming matches including the away match at Porto's headquarters.