I think that this season is going to be a season that Atletico Madrid are struggling to keep up while Barcelona and Real Madrid are competing hard for the La Liga title. Because I see nearly zero change about Atletico Madrid now. It is more difficult for them unless they add really qualified players to the team. I don't think Simeone would change his tactics much either.
Don't underestimate Atletico Madrid. Even if they didn't sign any top players, they are still a big team. I am sure that Atletico Madrid will compete for the title as well, just look at their result against Juventus, it seems Morata can be a sharp striker in Atletico Madrid this season. Simeone is a smart coach, he must know how to optimize his current squad. He already spent a lot of time with Atletico Madrid and is one of the top coaches in la Liga, he knows how to make his team stays strong.