How so?

OP is strongly implying that the 90% success rate for prosecutors is due to the courts being stacked against the defense. IMO that is where the logical fallacy is. Since prosecutors have wide latitude in deciding which cases to charge in the first place, it is very possible that the high success rate is due to prosecutors only charging cases where the accused actually committed the crimes being charged. Indeed, for the ~10% of cases where the accused is not found guilty, about 8% are due to the government dropping the case - only 1% are the jury acquitting the defendant outright. Thus, it would appear from that data that when the prosecution sees they are not likely to win a case, they drop it.

I'm making no argument that the courts or law are "fair", I'm just making the argument that quoting the 90% number is in no way evidence that courts are inherently biased towards the prosecution.

I think it’s a valid question as far as what the nature of that success rate is.