Atletico Madrid can still enliven the competition for the La Liga title even though Atletico Madrid did not add really quality players and Simeone did not change tactics.
But I still believe that Simeone will provide the best tactics for Atletico Madrid next season in order to compete with the two big teams (Barcelona and Real Madrid) for the title in La Liga.
Atlético Madrid is not a weak team. But the battle for the La Liga title will only be between Barcelona and Real Madrid. The likes of Sevilla and Atletico Madrid will only continue to fight for Champions League qualification. The Atletico Madrid squad had several weaknesses last season. But the Atlético management did not take the necessary steps to strengthen themselves. So I don't think Atletico Madrid are favourites for the title.
So far, I agree with you that the La Liga title race will most likely only be between Barcelona and Real Madrid. But the summer transfer window is still under way before it closes on September 1, which means Atletico Madrid still have time to bring in some of the players they are looking to strengthen their squad and participate in the La Liga title race.
The signing of Nahuel Molina and Axel Witsel still don't look right to deal with the power of Real Madrid and the changes of Barcelona. Although they brought back Alvaro Morata after a season on loan at Juventus, but apart from that they lost Luis Suarez, I think Diego Simeone needs to consider a new striker who will help Morata up front.