Barcelona's performance under Hansi Flick is indeed extraordinary, the coach did not need much time in his first season, he immediately managed the team very well as he has shown now, and indeed there is no need to doubt that Barcelona is a strong candidate team to win the UCL title, they only need to maintain their level of consistency in this increasingly tight schedule.
As a Madrid fan, I doubt Barcelona can win the UCL title this season. 
I admit that Barcelona performance is better now after replacing the new coach and in the end Hansi Flick proved that he is very suitable to be Barcelona coach even though he was initially doubted. But no matter how strong Barcelona is now, I am sure it will not be easy to get through all these challenges because there is still Liverpool who is much more consistent and has better quality players.
You are still saying because Real Madrid and Barcelona are top rivals. If Liverpool and Barcelona are the top best teams in the champions league competitions now, then it’s also very possible that they will also have the tendency to win the champions league when they go head to head with Liverpool in the finals. The two best teams in the competition are the both of them, so you won’t expect that they can’t do their best as a team to triumph in the competition. The two teams are keeping a lot of consistency in their games and if for any reason they happen to not be playing as expected, they will not be featured for the finals of the competition or amongst team with potentials to win the champions league competition.