Xavi was able to finish the season well in La Liga, but he failed to do so in the Champions League. Perhaps he has little experience in such competitions so far and it is easier for him to focus on one thing at a time. I think that in the current Champions League season Barcelona will not achieve great results again, because the competition is very big.
Xavi played in the Champions League last season and was later demoted to the Europa League and still got evicted in the end. He has experience both league while also focusing on his main goal last season which is the La Liga title which he won. After his qualification to the Champions League competition this season, he must have been preparing well to excel in both leagues. I’m expecting to see a big change in their game of play in both competition and won’t lose focus in any of them. Manchester City did it and won a treble last season, with a good coach this is achievable for Barcelona.
You can never say Xavi's experience in the previous Champions League as a player could ever help this player to have a better performance as a coach while coaching Barcelona.
If I'm not wrong, he never coached any teams in the Champions Leagues before and Xavi is a completely inexperienced coach in this tournament. Since he had no experience as a coach but got good results in La Lga with Barcelona we can expect to see the same thing from him in the Champions League.