There were about
124,000 Prophets, 25 with name are mentioned in Quran. 5 Prophets out of 25 mentioned in Quran came before Hazrat Ibrahim (A.S). Most of the religions were true, obviously would have been sent in its original form. Maybe later on distorted and corrupted by it follower. And it is illogical to assume that some follower had amended the scripture to include the morality part.
So we cant just decide which religion was corupted to which extent.
The concept like budhism is mix of different religious belief. To be accurate, Buddhism is a religion and Buddhists are worshiper, just check the wikipedia!