It's not bad but Brazilian players are given credits more than others just for being Brazilian talented players. Take Luiz for example, if he wasn't Brazilian with that weird look I doubt he'd cost that much.
How many Brazilian flops were there in the last 20 years? More than any other Nationality and the reason is because they are over-hyped, overrated and given too much credits from where they come from.
They're given more credit because some of the best players in history were from there. Because It's national team is the most iconic thing in world Football... Or was. So it will always be on the spotlight for it's own merit. Luiz being bought at that price was simply a reflection of modern football and overinflated deals. The shittiest player of any nationality today will cost you 30, 40M if you're not careful.
Why so many Brazilians were flop in the last 20 years? Two things You're failing to understand. 1. Brazil is a continent-sized country. In a 5 mile radius in a small town you'll find at least 10 kids who are good with the ball anywhere in the country. While a country in Europe might produce 10 players that plays for a top/somewhere top team, Brazil will be exporting hundreds, if not thousands every year. If 90 out of 100 players who at one point seemed to show some promise flop, it's much easier to notice that 90 than the 10 that made it. You produce more, the risk is obviously bigger. And then the expectation of living up to legends. Again, of course it's always gonna be easier to notice.
2. Price. In spite of what you think (Luiz), young Brazilians are cheap. Actually South Americans in general are cheap. There's a reason Barcelona has built their own schools in countries over there. Porto knows this and makes a living from buying them at ridiculous prices and making a huge profit. Add all to the fact people will always connect Brazilian players to their history, no matter what. So it's not a matter of being overrated, it's simply being what it is.