A better ranking in the standings does not guarantee a team can always win when facing a team in a lower ranking like Lecce, because a team like Lecce can also make a good performance that can cause the final result to be beyond many people's expectations. Although before the match started almost everyone might have tipped Roma as the winner in the match, but unexpected results are always possible to happen in the match.
That should be a strength because facing a weak team that is in a lower ranking can make it easier for a strong team to win the match. But back again as you said because football does not always run smoothly like the strategy implemented by the coach because in certain conditions the strategy does not work well and they actually lose momentum to achieve victory in the match.
Roma is favored to win the match because in terms of quality they are much better, moreover Roma's motivation now is how to get a win in the remaining matches so that Roma can achieve a much better standings position at the end of the season.