Yes. I understand the contrast in the equation, but the conclusions are similar. The Nazis claimed that genetic purity made the Germans formidable.
They also claimed that racial mixing was responsible for German weaknesses, so I could claim that your idea of Britain as a "nation of dicks" because of generations of pollution by nasty foreign rapists is "similar" to the Nazis. We can all take things out of context and label somebody we don't agree with as being "like Hitler and the Nazis." That's where Godwin's Law comes from.
I don't entertain for a second the notion that either you or Sojournerlumus have Nazi like delusions of British racial superiority. You just have a difference of opinion - he sees the ethnic diversity which stemmed from generations of invaders and immigrants as a strength, you see it as an explanation of Britain's faults. That doesn't make either of you "similar to the Nazis."
Does this mean that the US has greater cultural and genetic strength than Britain?
I don't know about greater than Britain, nor genetic strenths, but the US certainly has its ethnic diversity to thank for a lot of its cultural strengths.