It's not that you're wrong in that 200m is a great starting point to build a new squad. But you covered it in the first sentence. The current board (which Messi is trying to get away from apparently) are not the smartest on the transfer front.The way they spend their money is their problem. But 200M is a great starting point for a squad renewal nonetheless. We did it in 2017 when we brought in Bernardo, Danilo, Walker, Mendy and Ederson.
They blew a load of money on Dembélé when they couldn't sign Coutinho to replace Neymar. Despite the fact they didn't actually need to replace Neymar immediately. Then they went ahead and blew a load of money on Coutinho anyway, and they definitely didn't need him at this point. Then the next summer they blew a load of money on Malcom, who they didn't need, and Arthur who was talented and they DID need but they forgot to run a background check on. Then last summer they blew a load of money on De Jong who was not what they needed with Busquets still about and Griezmann who they absolutely did not need given he plays the same role as Messi. Lenglet is probably the only guy they've signed where you could say he's 100% been worth the money.
Even if we spent 300m on Messi, Barcelona would blow the money on 3 players; 2 of which they wouldn't need and 1 who turns out to be a dud. I'm thinking Alisson, De Ligt, and Mason Mount. And maybe if we're lucky they get Sancho before United do.