What does this sentence mean?
No one forced you to claim, falsely, that we had any "original text" or even a "received text".
Account for it? What does this even mean?
There were people around that had a lot of group mythologies to explain unanswered questions. Just like at every other point in documented human history.
What is meant by that last "they"?
Essentially, your point is this: We know for a fact that some stuff was said a long time ago and has been preserved to some extent.
To quote Christopher Hitchens, who put the natural refutation in its most apt form yet that I have seen:
"Yet again it is demonstrated that monotheistic religion is a plagiarism of a plagiarism of a hearsay of a hearsay, of an illusion of an illusion, extending all the way back to a fabrication of a few nonevents."
As far as the historicity of the Old Testament... faith is the answer, not evidence.
If you mean "contradictions" as in "real evidence contradicts the claims of the Bible", then this is quite false.
- There was no flight from Egypt. (source: "The Bible Unearthed")
- There was no wandering in the desert. (source: "The Bible Unearthed")
- There was no conquest of the promised land. (source: "The Bible Unearthed")
Many of the foundational events and sagas of both Jewish and Christian mythology are flatly untrue.
If you're interested in, say, a specific page, Google Books will let you read the section titled "A Conflict of Dates and Kings" (p. 56) and much much more.
Understandably, many of the "here's how it really happened according to actual, physical evidence" sections are not part of the preview. Don't give away the good stuff for free.