I don't agree with your interpretation of what O'Donnell meant to imply, except to note that I expect the worst possible interpretation to be taken by agenda driven mice.
However....you are still wrong in what you have said, and that's part of the reason I'm debating this thread. Because it simply doesn't do to jeer at what O'Donnell said, while displaying a similar ignorance on one's own part about the science.
The simple fact is that you don't know what the result would be of growing a mouse with 100% human brain tissue. You have NO idea. This would be a very interesting experiment. The resulting brain could be smooth, or highly convoluted. It could be considerably stupider than a regular mouse with a regular mouse brain. Etc.
And that's really what you are dealing with on an issue like this - high levels of uncertainty until the experiment is done. Some people have ethical concerns about such experiments. If not with mice, then for example they present a fairly good case against 100% human brain tissue being grown in a great ape.