It's funny how you can believe in Barcelona but you don't believe or consider Xavi abilities. In fact, Xavi is the head coach of Barcelona and of course, the results Barcelona get depend on how Xavi prepares and builds Barcelona to be better.
Xavi is a good coach with the potential to become a great coach, like Ancelotti, Morinho, Pep Guardiola, Arsene Wenger, Farguson, and others, but his current experience is insufficient for him to be referred to be a great coach, which is why he struggled in his first season at Barcelona.
Furthermore, the departure of Messi and other Barcelona players had some effects on the squad even before his arrival, but he is doing his best to develop a team that will be competitive, as he won the La Liga title last season ahead of Real Madrid. As a result, Barcelona's performance is dependent on his ability and effort, as he attempts to develop a strong and competitive team.
But yes, if we consider the teams in group H then of course, Barcleona has a big name there which is a favorite to win the group. But even if Barcelona were to qualify for the round of 16, it is likely that Barcelona would still find it difficult to go further. So maybe, it looks like Barcelona will only get to the quarterfinals, that too if they are lucky.
Barcelona is the favorite team to top Group H because they have a great squad and have more experience than any other team in the group. Although FC Porto and Shakhtar have some experience in Champions League football, Barcelona has the chance to qualify at the top of the group ahead of them.