Answer
Despite the Documentary Hypothesis, we know that Moses wrote the Pentateuch. All the circumstantial evidences point towards the fact.
However, evidences also show that holy men have edited the same.
Explanation
Jesus Christ asked a simple but very valid question to Nicodemus:
“I am telling you the truth: we speak of what we know and report
what we have seen, yet none of you is willing to accept our message.
If you don't believe when I talk to you about things on earth, how can
you possibly believe if I talk to you about things in heaven?” (John
3:11-12).
If Jesus is wrong in one natural thing, then we cannot trust Him in any of the spiritual things He said. This is the essence of what Jesus told Nicodemus.
If Jesus is wrong when He said Moses wrote the Pentateuch, then He could be wrong when He said He is the eternal Life giving resurrection to the believers!
Then we have no “justification” and “salvation” from God!
Jesus said Moses wrote the Pentateuch:
“Has not Moses given you the Law” (John 7:19).
Was Jesus wrong here?
Then we have no guarantee of our resurrection and eternal life because Jesus could be wrong there also!
Apostle Peter says that it is the Spirit of Christ that inspired Moses to write the Pentateuch (1 Pet 1:11).
If so, Lord Jesus Christ is in a much better position (than the so called “experts” who are removed by several centuries from the time) to witness correctly regarding Moses.
What the Pentateuch Says
“And Jehovah said to Moses, Write this, a memorial in a book,
and set it in the ears of Joshua” (Exo 17:14).
“And Moses wrote ALL the Words of Jehovah” (Exo 24:4).
“And Moses wrote this Law, and delivered it to the priests, the
sons of Levi” (Deut 31:9).
What Joshua Says
Joshua was the immediate successor of Moses. What does he witness concerning the writings of Moses?
“as Moses, the servant of Jehovah, commanded the sons of Israel, as it
is written in the book of the Law of Moses” (Joshua 8:31).
“And you shall be very strong to keep and to do all that is written in
the book of the Law of Moses, so as not to turn aside from it to the right or to the left” (Joshua 23:6).
Joshua ADDED/Edited the Book
Joshua has added and edited things in the Law of God written by Moses:
“And Joshua wrote these words in the book of the Law of God”
(Joshua 24:26).
Now we know who wrote the death of Moses (Deuteronomy chapter 34 and other portions) in Moses’ own book.
Kings to Copy the Law
There are clear instructions Moses wrote in advance to the future kings of Israel to write down a copy of the Book of Law:
“And it shall be, when he sits on the throne of his kingdom, he shall
write for himself a copy of this Law in a book, from before the priests, the Levites. And it shall be with him, and he shall read in
it all the days of his life, that he may learn to fear Jehovah your
God, to keep all the Words of this Law and these statutes, to do them”
(Deut 17:18-19).
The Book of the Law written by Moses was a practical book for day to day life for the Israelites right from Joshua.
It was not a conglomerate of Jahwist, Priestly, Elohist, Deuteronomist traditions. There was no enough time also for these traditions to accumulate because right from the time of Joshua, people were holding the Book of Law as the rule of conduct in their practical life.
Israel Forgets the Book
In spite of the strict rules of the Law, Israel especially the kings forgot all about it. At times they found accidentally the Book of Law in the Temple of God.
During King Josiah’s time:
“And when they brought out the silver that was brought into the house
of Jehovah, Hilkiah the priest found the Book of the Law of Jehovah by
Moses…..” (2 Chron 34:14).
A great commotion erupts when the King comes to know about it!
The same thing happens after the Babylonian captivity when the exiles thirst for God’s Word:
“And all the people gathered themselves as one man into the street
before the water gate. And they spoke to Ezra the scribe to bring the
Book of the Law of Moses, which Jehovah had commanded to Israel” (Neh
8:1).
So, there is a consistent record of history in the Scripture itself that the Pentateuch was written by Moses and the Book was the rule of law right from the time of Joshua onwards till now.
Conclusion
The OP may be “in agreement with the experts” who came about 3000 years later; but not with Lord Jesus Christ who inspired the writing of it.
Jesus witnessed that Moses wrote the Pentateuch. And He is the final word for a Christian.