Why?
Porto are simply mediocre as you come right now, not an effective shift as usual in finding future quality exports as before in replacing their profitable player sales. Best player is an underwhelming Martinez supported by a midfield of long shot hopes (only Herrera quality), sold Mangala who was super key in defence.
Benfica, I saw them in Emirates Cup, I can't stress enough how laughably bad they were, absolutely decimated as a club this summer, they have like 3 good players left (4 If Enzo stays, doubtful) , way top many green youngsters signed and horrid defence .
Atletico we shouldn't need to mention what an annoyingly formidable team they are tactically, physically and quality wise. Historic season and they covered their departures rather well with Mandzukic, Siqueira, Oblak and Griezmann. Their biggest loss is your countryman, but otherwise they did a good job of adding quality to an already exceptionally build team.
So tell me, how are the Portuguese harder opponents then them?