The position of being the favorite team or not will certainly greatly influence who Arsenal will face next if they succeed in eliminating Porto in the round of 16.
My prediction is that looking at the existing teams, there is a very big chance that Arsenal will meet one of these strong teams, and if that happens it will be very difficult for Arsenal to advance to the next round, but before that, they have to be able to overcome the Porto team which is quite good even though many people predict that Arsenal will beat Porto, but in my opinion, the chances of both teams are the same, because Arsenal can sometimes appear disappointing, such as when they lost to West Ham in the English Premier League.
The playoffs are a very difficult stage, everything needs to be decided in two games, but perhaps for Arsenal there is an advantage in that they will play the first game at Estádio do Dragao, in case of a win or a draw their chances of winning the return match will be higher.
I don’t consider Porto a weak opponent, they are capable of beating Arsenal, especially if you look at Arsenal’s latest results in five games, they won only once in the match with Brighton, they lost the matches with Aston Villa and West Ham, and they drew with Liverpool and PSV , so Arsenal may be in decline.
Arsenal have the advantage of playing the first leg at home to Porto and they should be able to prove their capacity. It's not easy to face the cheers of Porto fans and it can bring down their mentality. But what is clear is that even if Arsenal fail to gain an aggregate advantage or even lose to Porto, at least it will be an aggregate with a narrow margin and not a landslide. So that when the second leg is held at the Emirates Stadium, Arsenal can still reverse the aggregate or even host Porto until the penalty shootout.
Arsenal's performance in the domestic league is quite poor and that could be a stumbling block for them before the first leg starts. The Gunners squad's readiness must be arranged neatly considering that the Champions League is more difficult than the domestic league that they often encounter.