I don't understand what's funny. Or are you arguing that the MBTI doesn't claim to be based on Jung's work? And your 'round Earth' argument makes no sense.
Some people claimed that the Earth was round. There was no "facts" or "science" yet to back that up. It was just a theory until proven otherwise. Yet the Earth was still round, despite what all of the non-believers said.
As to why I find it ironic that you are defending the criticisms? It's simply that you're basing your opinion on the belief that Meyers/Briggs misinterpreted Jung's work; as though Jung was the final authority to begin with. Even if they are wrong, who's to say he wasn't either and that neither party is "right" in that regard? Look at how popular Freud was for the longest time. His word was god in psychological circles, and now much of what he said is being dismissed. And who knows, maybe they saw the flaws with his work and tried to correct what they thought improbable or inaccurate? You don't have to be a genius or certified scientist to make contributions to science.
I never made any claims about MBTI to be thoroughly valid, although there's a lot more to it than simple parlor tricks. Even though it generalizes too much, a lot of the desriptions
are relatively accurate in a macro sense. I've also read the various statements about how people retest differently even within a short period or that they've read a completely different type description (other than what they tested as) to people they knew, who agreed with the descriptions fitting. Hurray for them I guess? I know from "anecedotal" evidence that it isn't the case for everyone at all.
What concerns me the most about what they claim though is that they say that you are born that way. They make claims that it's nature and not nurture that influences us the most, yet I have a lot of misgivings about that. I feel like I am the way that I am more because of the environment I grew up around rather than simply being this way from the start. The same thing applies to two of my best friends. I can't really see them being the same (or even similar for that matter) people, given opposite upbringings.
MBTI makes claims of having actual test subjects to refute this, especially in the case of identical twins, but I'm not completely sold on that yet.
Here's a pretty decent argument against it. I suggest you also read the replies.
http://www.theguardian.com/science/brain-flapping/2013/mar/19/myers-briggs-test-unscientific