For Liverpool and Manchester City may be a little more convincing because these two teams have good players and also both have experience in the Champions League. Arsenal also have great players but they are not mentally enough when competing in the Champions League and maybe this mindset they need to fix so that Arsenal can provide competition while playing there. If this condition is unable to be created then I doubt Arsenal's ability when playing in the Champions League against a far more balanced team.
Come to the FC Porto headquarters is not easy even though the quality of them is a little more draw, but FC Porto is a team that always plays in the Champions League so that their experiences are much better. Arteta had to struggle to get points in the match to make it easier for them when playing at the Emirates Stadium.
Playoff games are always more difficult because the responsibility is higher, any mistake can be fatal, so teams play more carefully. This has always been the case for Porto, they are very dangerous at home and I'm a little surprised to see 4.5 at Porto at home. Arsenal is considered the favorite in this match with 1.78, but I would not risk betting on Arsenal to win in this match.
There is still more than a month before the match, so it is not worth assessing the current form of the teams. Maybe during this time Arsenal will be able to improve their game, since they are now in a clear decline, the opponents were not the easiest, but this does not justify so many defeats.