Inter vs Arsenal is another interesting match, you see that Inter only conceded 1 goal from 8 match, that's insane how good is their defense.
We cannot just assume that teams will meet each other in the round of 16 based on their positions in the standings. The draw will not be done at this time; I believe we will have to wait for the other teams in a playoff to finish their games before they can schedule the next matches with the other teams who qualified through the playoff. I believe Arsenal and Inter Milan will not meet each other in the following round of the game, but we'll see what happens.
Barcelona tried their best in this match, though Atalanta did well too, and they tried their best to see that they win the match, but unfortunately it ended in a draw. I think this could be a very good result for them if they win the match, although the result did not affect Barcelona since their position in the table is still okay. But Atalanta were trying their best to see that they win so they will qualify. But you are right; they can still do better in the coming round. Since they are not a weak team.
Barcelona did not give their all in the game against Atalanta, they could have won, but they appeared unbothered even if they lost. Atalanta pressured Barcelona in the first half of the game, and I thought Barcelona would lose in the second half due to their many attempts to score goals. However, the match ended in a 2-2 draw, which did not affect Barcelona's league table position; they finished second and advanced to the round of 16. Barcelona must play to the highest level in the next round, otherwise, they risk conceding a goal in an important match and finding it tough to equalize.