Mississippi <3

[Viking]

Well, reccessive genes will probably survive on and manifest, but now more as a spread out and more rare cases. So in the case of the global pandemic, that means that the average resistance goes up, while it goes down in some regions.

It slows down the development of subspecies, while having a significant base to have a resilent spicie, since we got some many who get children, with their own variation.
Compare with what we do with breeding, when only a selected few can breed, that would be to have chosen fathers that breeds millions of children. That's good for selective traits, but not for resilence. Ethnicities ends up in between.
That should mean that humanity as a whole benefits from hybridization, unless we're intending to specialize humanity and also your children, as commented above (the mixing reduces the number of poor genes on average).

Individual ethnicities tend to have a rather large variation as well. It would be favourable to have parts of societies survive rather than a few individuals here and there. Though, a question is how effective pandemics may become.

Irrelevant due to mutation.

Muations are individual. Ethnical traits belong to...ethnicities. If the relevant recessive gene becomes largely inactive, a few scattered mutations are not going to make a big difference.