Both of Monaco vs Barcelona and Atlanta vs arsenal are not a huge surprise as many people are portraying it. Atlanta were the Europa league champions beating last season Bundesliga winner Leverkusen. Monaco too is a second team in french league last season. Both of Atlanta and Monaco were playing at home. Manchester City vs Inter Milan was much surprising for me. But its first round of league and there are plenty of matches to be played.
Indeed, Monaco is a top team in the French league, of course that's why they entered the UCL. However, to be honest, sorry if compared to Barcelona, their team strength should not be balanced. Barcelona should be superior in all lines. However, unfortunately, it is not because Monaco is very strong, but because Barcelona only played with 10 players from the beginning of the match. It was really difficult, 10 vs 11.