Do we even know what Pelagius taught except through his critics? They are hardly an unbiased source.
I reject the concept of original sin. It is toxic. People sin through their actions, not inherited from someone else.
I recommend:
A Better Atonement: Beyond the Depraved Doctrine of Original Sin
by Tony Jones
https://www.amazon.com/Better-Atonement-Depraved-Doctrine-Original-ebook/dp/B007MD0AK8