Well, it's difficult to reliably study oral traditions in depth in history textbooks because... they aren't written down.
But the part about preachers trying to quote the Old Testament or problematic passages from the apostles literally to justify bad things is quite frequent.
I've read a few books about it, but I take the history of religion with a huge grain of salt (they have too many incentives to distort what happened). So, the only thing I can analyze is the present.



It's wrong. Religious texts do change due to translations and having multiple editions (even in the same language), but they change at a far slower rate than they would in non-written form.
If a reformer tried to argue that practices such as animal sacrifices were not Islamic, for example, scholars would just point to one or two verses and they would be shut down.
The only reason sacred texts seem to "evolve" at times is because believers find alternative ways to interpret them when the teachings are morally troubling and universally condemned, something possible even if the text doesn't change much.
Memorizing word-for-word was possible using techniques such as mnemonics or poetry, but it was difficult for extremely long passages without effort, and regular review was needed to avoid forgetting them.