Again, RM was top spot before CR7, if anything they lost a place to us with him.
They are far more established historically than we did before Messi. I don't think it is correct to compare. Never mind they still had many of core players who win 4 CL titles with them, and a manager who is a football brand by himself (due to playing career) , and 4 CL titles in 5 years before CR7 left. Our last one will be 6 years when Messi leaves
Same with Manu, who is playing in wealthiest country football wise, while having a big Asian fanbase too.
And even Manu had Rooney as their superstar poster boy from their glory days, and when declined they paid kings ransom to get Pogba.
Football is a game of stars, and Barcelona has been always a galactico type of club. Hell, Gaspart once argued we are the real top club of 20th century because we had more stars than RM.
It is huge part of club identity.
Who are you gonna put in front of camera when Messi leaves? Fati? flops like Coutinho-Griezmann? who are close to their 30 anyway and never did play well with us?
Busquets and Pique who needs top be shown the door before Messi?
The club will have to prioterize big signing if they want to remain top 3 in revenue within the next 3-5 years.