The philosophical idea of hard determinism is hard to believe for most people. But when you understand it correctly (check The Scientific Buddhism) and accept it, you will view the world totally differently.
When the Buddha was living, he led a group of people to practice his teaching. Other people also contributed ideas to him. So Buddhism was a team work from the beginning.
The Buddha didn’t write anything about his teaching. Buddhists wrote Buddha’s teaching later. More and more people involved and contributed to Buddhism. People may have some different ideas, so they have different schools.
At least some of the Buddhists accepted hard determinism in history, as Charles Goodman described in his paper “Resentment and Reality: Buddhism on Moral Responsibility”.
The hard determinism tradition in Buddhism is valuable for today’s people.