I saw a quote from Keita saying he agreed with the line, "Egyptians are Egyptians."
Can you provide a source for that quote?
That's a rather simplistic statement. In the video I posted Keita said we do have to acknowledge that people who were non-Egyptian in terms of their ethno-nationality came into the country. He would not have mentioned this if he didn't feel this non-Egyptian migration was significant. In literature he states that he feels cosmopolitan Lower Egypt may not be representative of the indigenous population and makes the statement that small steady migration over a long period of time combined with the effects of polygamy can cause a significant change in the gene frequencies and physiognomy of the population. So he clearly implies that there has been a major genetic influence on Egypt during historical times citing the Greco-Roman and Islamic periods specifically.
One thing I do find of interest in the video is the statement that the physical diversity of Ancient Egypt would have been the same as the present. He also says the Egyptians had mixed ancestry since the pre-dynastic period. Now ofcourse that begs the question, mixed with what? Also mixed to what degree? In personal communication with me he says that the typical Upper Egyptian to Nubian skin color would have been the model in most of the country suggesting that Ancient Egyptians were primarily dark-skinned. Could the Egyptians have diversity like that of the present and be primarily dark-skinned? That's possible. It could just mean that diverse phenotypes were present in the Nile Valley since the pre-dynastic and that there may have been a light-skinned element in Egypt during the Dynastic period establishing diversity but just not to the level that there is today.
We have to be careful about attributing statements to scholars that they did not make. Keita never said that light-skinned people were the predominate people of Lower Egypt or that they had been in place since the Paleolithic period. He said that we could draw conclusions from modern DNA studies about populations movements going back to the Paleolithic period.
As I recall Brace et al. (1993) were the ones who came to the conclusion that Egyptians were Egyptians and had been in place since the Pleistocene, unaffected by invasions or migrations. They also repudiated the views of Afrocentrists taking particular aim at the work of Cheikh Anta Diop. Keita responded to Brace et al (1993) in an article published under his original name (J.D. Walker) titled, "The Misrepresentation of Diop's Views."
He made alot of criticisms of Brace's study within that article.
Having read several of Keita's articles I can safely say that his conclusion is that Ancient Egypt was a fundamentally African civilization and that Egypt underwent significant cultural and biological changes over the past 2000 years since the time of the Pharaohs. I think he and Ivan Van Sertima are in agreement that the Africanity of Ancient Egypt was diluted by European and Near Eastern elements resulting in the modern diversity seen today.