Who said it would necessarily be worse? The most important thing is to keep the other Lionel.
When a team loses its best player by a large margin, it's hard to talk about the positives. Especially when that player is Leo Messi. Inimitable. One of the best in history. And for many, the absolute best. Leo left the Argentina national team. He left after losing the World Cup final. However, this defeat does not cast a shadow over his brilliant career. Just like the fact that he lost two of the three World Cup finals.
Wait, wait. Three World Cup finals. Three. And, most importantly, there is one victory. Yes, there are also defeats. But, again, Leo has three World Cup finals. And he has a title. So, no matter how hard you try to find faults, you will not succeed.
So when a player like that leaves, sadness fills everything. For some it's sweet, for some it's bitter. But sadness. The realization that things will never be the same again.
And that's true, things won't be the same as they were before. But who said that things will definitely get worse? In other words, yes, definitely. But why immediately worse?

Leon is great: he could make the difference at any moment against any opponent in any game. However, no matter how great his teammates were (and they have been great at different times - Argentina is generous with talent), everything ultimately revolved around him. Perhaps this is inevitable when you have a player like him. It even makes sense. But it also has its understandable drawbacks.
The star player of the team is the obvious choice. Both the team and the opponents know it. So, cover the star player and life will immediately become easier. In such a situation, the other players, those around the star, can step up. But Argentina has had huge problems in this regard for years.
Great players from the best clubs in the world came to the national team and became Leo's entourage, in the worst sense of the word. They immediately forgot that they were also capable of anything. It was as if they were deliberately hiding their skills so as not to inadvertently undermine Leo's dominance - the fact that he was a priori superior to everyone. His teammates, literally pushing each other aside, gravitated towards Messi, like little puppies, their eyes still closed, gravitated towards their mother.
Until Lionel Scaloni came along, there had never been a coach who could properly combine these two personalities, Messi and everyone else. But Scaloni did it. Scaloni, who accidentally got into the national team. After the defeat in the 2018 World Cup, Jorge Sampaoli was fired and Scaloni was appointed interim coach until they found a full-time head coach. You know what happened next.
Scaloni, like Messi, lost the last World Cup final. But, like Leo, this does not cast doubt on him. By the way, they are both Leos. Lionels. Logically, they should be Lions, not Leos. But that is just a detail. If Lionel Messi is a Leo, then Lionel Scaloni should be one too.
Scaloni did the most important thing: he got Messi and the others going in the same direction. Whereas before everyone was pulling towards Messi, under Scaloni's leadership Messi and everyone else were pulling forward, towards victories. The team, of course, remained focused on Messi, but this turned from a negative into a positive. His teammates continued to serve Leo, but Scaloni somehow convinced them that they were just as important in their own right. And that Messi was helping them as much as they were helping him.
Scaloni's arrival in the national team is a reward for Messi for all the suffering he has endured in the blue and white jersey. Before being appointed coach, Leon had not won a single trophy with the national team (the Olympics do not count, as teams do not play there with their strongest squads), had lost four finals and had announced his retirement twice.
First in 2016, after losing to Chile in the Copa America final. Then in 2018, after being eliminated in the round of 16 of the World Cup. Yes, officially Messi did not leave the national team in 2018, he simply took a break. However, it seemed that he would no longer be in the national team: it seemed that if he had changed his mind and stayed in 2016, he would have definitely left. But life turned out differently, and now Messi has officially left the national team, having won the World Cup trophy, two victories in the Copa America and even a victory in the Finalisima.
Another Leo, Scaloni, could also leave the national team. After the 2026 World Cup final, the coach announced:
Scaloni says that building a new team is the main task of the Argentina national team. Messi is gone, he will leave. He is great, who is arguing? But that's it. Leo is no longer in the national team, but the national team itself remains. And it seems that Scaloni is ideally suited to build a new team.
He has achieved enormous success. Consequently, he now enjoys an equally enormous reputation. These successes did not just happen: they are the result of Scaloni's proven coaching skills. Finally, he is well aware of the specifics of working with the national team. It is a unique job, and not everyone can cope with it.