can we dream up any defence at all for them?
Well, the obvious one would be God. He caused the flood, and wanted the animals to survive, and since a genetic bottleneck can be detrimental to a species, he "fixed" them.
The supposed "Supergenome" combined with extremely different genetic laws in the past, as foreveryoung posited, might solve some of it.
As you say, claiming that since everything has the same genetic bottleneck, you might not notice it since everything would look the same, might work for non-scientists.
Unfortunately, the third claim comes from a misunderstanding of genetics and the first two are offered with no (and in the first one's case, no possible) evidence.