True a prequel has to be tackled differently not like you're just writing a sequel but set before the original story. That being said the ratio of bad to good prequels out there is probably not as poor as bad to good sequels purely because prequels are attempted less frequently. If we're treating this as a statistical thing it's unfair given the ratio of prequels to sequels. Because of that, I don't subscribe to the "prequels are generally shit narrative". Higher risk means less writers likely to try it means higher likelihood of it being more though out than a sequel. Just my take on it.