Why and how was the Hindu religion that evolved from Vedism able to overcome the
challenges posed by Buddhism and Jainism,
whereas Greco-Roman paganism could not
ultimately prevail against Christianity?

The answer given below.

Explanation:

Hindu religion was able to survive even after it saw the emerging of Buddhism and Jainism because they all had basic principle which interconnected to Hinduism.

The Greco-Roman religion could not survive against Christianity as they worshipped many gods and goddesses. It was polytheistic religions of the Mediterranean, mainly practices in Greece and Rome from ancient period.

Christianity was a modern religion whose ideas and principles were different from other religion. They saw traditional polytheistic religion as paganism as people worshipped many gods.

Christianity is Abrahamic faith and followers monotheistic. Monotheistic word  used to describe the belief worship of only one god.