How might the lack of a single founder result in Hinduism changing more over time than other religions?
Hinduism has not changed at all. the core values, teachings, scripts and practices remained the same. It is a very futuristic and accommodative religion unlike other conservative ones based on one preacher or a script. There is no fundamentalism in Hinduism.
The single founder of any religion has contributed to one sided thought process leading to being closed to thoughts beyond him. Hinduism does not suffer from this limitation. Multiple scripts and many gods and goddesses added value to the religion and unified the world of Hinduism.
To experience, the unity in diversity in Hinduism, visit India.