Arsenal couldn’t win any trophy, so I don’t understand what you meant by Arsenal had a great season. Arsenal didn’t achieve anything, the only thing which I will say they achieved is qualifying for the champions league next season, but apart from that there is no achievement for Arsenal. If they were able to win at least a trophy, then I will say they had a great season.
Overall Arsenal had a good season as they finished 2nd in the Premier League, we can't ignore this achievement because of the fact that they beat strong teams like Manchester City who always dominate. Another achievement was Arsenal reaching the semifinals in the Champions League. we know no Premier League team has made it to that stage even Madrid and Bayern Munich only reached the quarter finals well, it's not an exaggeration if someone says Arsenal have had a good season even without a trophy yeah at least better than the previous season.