These comparisons across different leagues are not trivial sometimes because so many factors come into play. You could also mention Atletico Madrid as a strong team even when they didn't perform as good as they did in the seasons before. But when you take Sevilla and see how they eliminated Manchester United from the Europa League, it becomes obvious that a comparison isn't easy. Should we consider the position in the table? Then it is Manchester United who were much better, but when we see how Sevilla won against them in the home game, the whole comparison should be worked out differently. I agree that the Premier League is better overall, but in matchups between teams from both leagues some of the results could be much closer than a general comparison would suggest.
One striking area of comparison should be the financial value of the league. And the English Premier League has been the most expensive in Europe. In terms of sponsorship deals and TV rights, the EPL is number one. And this also has the highest number of viewers. An example is my country where the EPL is the most watched and has the highest fan base. It has also been called the most exciting league in the world and it has attracted some of the world's best footballers. I might not be right, it has one best football organizing bodies that have fewer scandals compared to other leagues.
Barcelona's current club concern right now shouldn't be about signing a high profile players like Kylian Mbappe when the club's financial strength is on the decline.
They have a manager in Xavi Hernandez who believes so much in his young team to deliver spectacular performances just like they've been doing since his arrival as the club manager. Barcelona should critically look in to what they can do as a club to help their and recover from their financial ruins
I also don't think that Barca should consider signing Mbappe considering their financial standings. But signing players also have some benefits outside the pitch. If the club has done an extensive market analysis and discovered that the French player can attract other financial benefits like lucrative endorsements and sponsorships, then it is a risk worth taking. I know that Mbappe will bring more attention to the club which could affect their financial base positively. But if it is all about pitch performance, I suggest that the club still maintain its strategy of buying cheap players until they become healthy financially.