That's... I mean yes that is how it works but it's also not.

It doesn't matter if you do it seventy billion times, the issue with cosanguinity is the increased risk of passing on mutated alleles which would have significantly less risk of being passed on in a non consanguinous coupling. The more consanguinous the more risk of sharing a mutation, hence the greater risk. As soon as you have a mutation you have the risk. If you don't have a mutation you could go full Ptolemy without any problem. Theoretically at least. Of course everyone has minor mutations in their germline so consanguinity is always risky. In that sense inbreeding is both much, much, worse and much better than having kids in your late 30s.

But there is genuinely a problem with consanguinity in some immigrant communities. If they don't marry and reproduce outside a specific social structure, and there's only like 20 of them in the country, then by necessity you end up with consanguinity.