Terry:
I don't think we're at odds here. My point was that all religions, all sects and divisions within those religions, seem to have changed, adapted, fiddled with, their doctrines and beliefs throughout history. One of the strongest examples is Islam, which claimed (uniquely, I think) to be the final revelation. Didn't turn out like that.
To me (a personal view) any deity which inspired a religion but couldn't or didn't maintain the original message is hardly a deity at all.
To expand on my point about the relative 'newness' of religions: I live in West Wales. Nearby is St Davids cathedral, about 1000 years old (king Alfred 'the Great') was involved there. It was a 'holy site' about 1400 years ago. You can see the effects of the Reformation (a relatively recent 500 years ago). Also St Govan's chapel (800 years old) built on the site of St Govan's rockface cleft hermitage(1400 years ago) (was he Sir Gawain of Round Table fame?). The local churches in my town are 800+ years old, so went through the Reformation.
There is no doubt that many local religious sites pre-date the Roman invasion and were pagan/druidic. There is still a noteable pagan/wicca presence here.
In my small town there are memorial sites where 'heretics' of different persuasions were burned to death.
May I recommend that you read the 'Shardlake' novels by C J Sansom? Tremendous read, and sets the scene for Reformation-era England.