If you want evidence of this, just read the Gospels, compare them. You will see large swaths of text that are identical.Funny, I've never read that before. My guess is that you are getting your information from those biased against the Church.
Can you prove that "large parts of the Gospel of Mathew and the Gospel of Luke were just copied directly from the Gospel of Mark"? Or is this merely speculation?
If you want further evidence just ask your local Priest. The fact that that the Synoptic gospels copied text from Mark is widely acknowledged even by the Catholic Church.
If you want internet links, search Google. Look at different sources, and by all means go ahead and give priority to Catholic sources if you wish to, you will still find what I am saying is true.
Bible.org - hardly biased against the church
https://bible.org/article/synoptic-problem
It is quite impossible to hold that the three synoptic gospels were completely independent from each other. In the least, they had to have shared a common oral tradition. But the vast bulk of NT scholars today would argue for much more than that.3 There are four crucial arguments which virtually prove literary interdependence.
catholic-resourses.org - you can't tell me this is biased against the church.
http://catholic-resources.org/Bible/Synoptic_Problem.htm
The similarities between Matthew, Mark, and Luke are so numerous and so close, not just in the order of the material presented but also in the exact wording of long stretches of text, that it is not sufficient to explain these similarities on the basis of common oral tradition alone. Rather, some type of literary dependence must be assumed as well. That is, someone copied from someone else's previously written text;
There are dozens of other sites I could give you links to, but I have to go right now. Take a look at these, and do your own research. What I am saying is hardly new or controversial.