I think it was Ashley Montague who famously opined that "there is no such thing as race". I choose to understand this to mean that race is not categorical, but circumstantial, and always in flux.
There has been a change, of course. At one time no doubt, one could speak of the Welsh and the Scots as races, and I believe that this was in fact the way of thinking, because these were fairly stable breeding populations.
As the boundaries between such populations grew more distant, we were left with the more modern conception of a handful of distinct, more or less continental, races.
But I agree with Ashley Montague's sentiment that these are not categorical distinctions, any more than the distinction between the Welsh and the Scots.
Yes, without “stable breeding populations” the concept of race is losing it’s utility.
Also the localization of races led to cultural distinctions that could be made between them.
Nowadays the concept is pretty much of use to just Democrat politicians and, very occasionally, to doctors.