How sure can you be? We can only call the favorite at this point but pointing out who wins is just speculation on our part. The points Barcelona uses in surpassing Atletico Madrid are considerably enough to limit the assurance that they will win the league. They lost the ability when they faced Barcelona and was unable to secure the winning points, the fall started from there, and a different scenario if Barcelona will be willing to release some points within the remaining games to put Atletico Madrid back in the race.
It is still quite difficult to determine who will win the La Liga title because there are still several games left, even though Barcelona are currently leading with one game in hand, it is not certain that they can win the La Liga title. We can only name the favorites as you said but regarding the final result we cannot guarantee for sure who will be the champion because one of the two teams has to make that move based on their results and performance.
Atletico Madrid may be getting harder because their chances are getting smaller but Real Madrid still have a chance. It really depends on how both teams can maintain their winning streak in the remaining matches because if they make a mistake in just one match, it can change the map of the champion candidates.