After Arsenal’s qualification from the round of 16 to the quarterfinals, that’s when a more bigger challenge awaits them to accomplish to continue going further in this competition. FC Porto might have given them a very tough time before making it to the quarterfinals, but at this stage they should be extra prepared to have a more challenge pose on them before making it to the semifinals. I don’t see any team in this round that will be faced with Arsenal for them to have an easy passage to the quarterfinals, they will definitely fight their way through with so much hardwork for their dream to come true.
You didn’t mention Bayern Munich amongst the team they may be scared to face in the quarterfinals alongside Manchester City and Real Madrid. They could pray to have a team like Arsenal and Dortmund but not. Barcelona and PSG whom they also have good records in the competition for long now also. I won’t underrate any of this teams too much when they’re faced with Atletico Madrid to play. They could get a more leniency when matchup with Dortmund or Arsenal, but for the rest of them, it will be as tough as hell for them to pass through into the semifinals. The next round of the competition will be entirely different and full of drama irrespective of any team any of the teams will be facing.