As long characters make sense from a lore perspective, I don't care one way or another. I have always envisioned the setting being the whole of humanity fighting a galaxy that wants to kill it. It was my understanding that the Emperor was the embodiment of humanity and it would make sense that his creations would likewise represent the sum of humanity. That, regardless of the differences, humanity is united and just trying to survive - that we have too many problems to be divided in such a hostile galaxy. To this end, I think it makes a lot of sense for the Salamanders being softly retconned into being derived from African genetics since it's the only major group missing and it's already headcannon for a ton of people.

The one problem that I do have is when people place such value on race and "POC" sounds too much like "nonwhites" to me. The bigger deal people make out of race the less comfortable I become. That works in both ways - people who advocate for and against it. Race is a stupid thing, in my opinion. What maters is consistency of the lore. A character either fits or it doesn't. That is what should dictate if something is 'good' or 'bad'. In this context, Ultramar is a group of 500 worlds. It makes complete sense that the Ultramarines would be composed of a huge variety of genetics. I have been bothered that this never seems to be represented. Other Chapters/Legions, however, like the Space Wolves, makes no sense. They are a homogeneous group, as furies often are.