I think its also worth noting that as Tolkien's academic career began, it was popularly (and erroneously) believed that humanity originated in the Caucasus Mountains, and that non-white peoples had degenerated into various subraces: the mongoloids of Asia, the congoids of Africa, etc. An example of how deeply this theory penetrated is the original name for Down Syndrome was Mongolism, out of the (erroneous, ableist, racist) perception that due to the characteristic facial features of people with this condition, they had genetically "degenerated" in similar fashion. As evidence for humanity's origin in Africa mounted, towards the end of Tolkien's career, some theoreticians suggested that *Homo sapiens* had evolved from *Homo erecteus* five separate times, including in Mongolia, once again reinventing the "mongol type" as a "scientific" racial category. Suffice it to say that this is, ahem, very racist bunk anthropology!
With this context, when Tolkien calls the orcs "degraded and repulsive versions of the (to Europeans) least lovely Mongol-types," he's not simply suggesting that they look like people from Mongolia. He is invoking this whole body of pseudoscientific literature to situate the orcs in relationship with Europeans.
HOWEVER--it is notable that Tolkien refuses to claim objectivity here. He says "least lovely (to Europeans)," which is significant because one of the central claims of the Caucasian theory of human evolution was that people from the Caucasus were the most beautiful, and therefore least degraded strain of humanity. Tolkien's academic work in philology had already punctured the theory somewhat---it's finding that European languages evolved from a common stem somewhere in India undercut any claims of a separate European evolutionary track or special descent from the Caucasus. So while Tolkien may be evoking these theories and be conversant in them, it certainly seems like he doesn't believe them, or at least the objective racial hierarchy they propose. Tolkien's famous letter to his German publishers is further evidence of this. And it is also worth mentioning that Asian and African people exist in Arda and are not equivalent to orcs, and are portrayed as deserving moral consideration---for example, Sam's reaction to the dead Haradrim soldier in Ithilien, and his speculation over what lies or threats had led him on the long march from his home and if he would rather have stayed there in peace.”
What is the take-away to all of this? I think it is clear that Tolkien was a racist in that he believed that race was a real, measurable thing that existed in the world, and that some of the terminology of this worldview carried over in his writing. But it is also clear that, to the extent that it was possible for someone of his station in his time, was not possessed of racial animus or racial superiority. He was opposed to the British Empire, had the "hatred of Apartheid in his bones," and rejected the supposed objectivity of scientific racism, both in England and Germany. He is a complicated man, and his work is complicated too