With both Atletico and Barcelona improving and dropping so far, the reality is that they still have a chance of finishing in the top four, so if it was just about overtaking it would be fine if they could finish in the top four in the end.
Sure, both Atletico dan Barcelona still have an opportunity to be back at the top four on the table. Point gaps among the teams in 4th-8th aren't quite small, their positions can be changed in 1 or 2 matches only. I am not surprised if Atletico or Barcelona suddenly is in the top four again in the next month (January). I assume Rayo Vallecano will be out of the top four soon because they may lose points against Atletico, Barcelona, and Real Betis in January. It is a real chance for Atletico dan Barcelona to be back at the UCL zone.
Check La Liga fixtures in January 2022https://www.footballwebpages.co.uk/spanish-la-liga/fixtures-results/januaryThe opportunity to play in the UEFA Champions League next season is still wide open for Barcelona, but that's how they can take advantage of every game in La Liga. There is still plenty of time to improve their performance. I'm sure they'll be able to get out of what they're going through now.
Apart from that I agree with your opinion, they are only a few points behind, it is not impossible with 1 or 2 games they can improve their position in the standings.
There are still 20 more games to be played by Barcelona, so there is still a very big chance for Barcelona to enter the top 4 to be able to play
in the Champions League next season. But to be able to compete for the La Liga trophy this season is impossible for Barcelona, so indeed finishing
in the top 4 is a reasonable target for Barcelona to achieve this season. Moreover, the performance of Atlético and Real Sociedad, which is
above Barcelona, continues to decline. While for Betis and Rayo in the next few games it is possible to lose a lot of points. The team that is
above Barcelona maybe only Real Madrid will play consistently, even Sevilla who are in second place I doubt they can play consistently in the next
few games. Most importantly Barcelona just focus on being able to win match as much as possible, and try not to lose a lot of points. That way
Barcelona can definitely finish this season in the top 4.