In the Premier League, maybe Arsenal is still the favorite in competing for the trophy, but in the Champions League it is a big competition different to the Premier League. In the Champions League there are still Real Madrid, Bayern Munich and Inter Milan who are still Arsenal's tough challenges, maybe Arsenal can beat Manchester City in the domestic league but as we know, Manchester City's performance in the Champions League is very strong, they are very focused in terms of attack and defense, they are also very strong, so I doubt that if Arsenal faced Manchester City in a different competition, whether Arsenal could beat them.
Fighting and beating Porto in the second leg should be able to prove for Arsenal in the Champions League which is indeed they are underestimated, for now Arsenal must be able to optimize the second leg in order to continue their journey in the Champions League this season, seeing Arsenal's performance in the league which is so very spectacular, of course, is inversely proportional when they played in the first leg and were defeated by Porto in the final minute Match.
What you are saying is true that the atmosphere between the Champions League and the Premier League is very different and maybe even the journey of a club in the Champions League will be more difficult than they play in the league, but somehow when I see Arsenal play at home I am quite sure if Arsenal will be able to beat Porto, Arsenal home record this season is quite good and even they perform quite solid when playing at Emirates Stadium, I don't think we can underestimate Arsenal just because they lost 1-0 in the first leg, especially when we saw often Arsenal make surprising comebacks when playing at Emirates Stadium so far.
Yes Arsenal have to fight hard to prove to everyone that they are still worthy of competing in the Champions League, Porto is not a club that Arsenal can underestimate, they have experience in the Champions League and have quite a good history so Arsenal must improve their performance not only in domestic league but also in the Champions League so that he is not underestimated. Of course Arsenal is still the favorite club in this round to be able to beat Porto because of Arsenal's good performance in the Premier League for that Arsenal must prove it in the second leg and remain focused so as not to make any mistakes that cause they suffered a defeat like in the first leg, to be honest, it was very painful for Arsenal because they failed to win.
Therefore, every big club is playing optimally here, we can see that Manchester City's performance was inconsistent in the Premier League, while Manchester City's performance was very strong in the Champions League. This is not because Manchester City is having difficulty in their own league, it's just that they are struggling a little hard in the competition. This is so big that it is a little unfocused in the domestic league, but because the Manchester City players have returned they have now returned to their best performance and are quite stable in all competitions.
And yes, I also don't underestimate Arsenal, their performance has been very impressive lately. Especially when they play at home and I'm also quite sure that when Arsenal plays at home they will play strong and I think they will also be able to beat Porto maybe not with score big.