It still doesn't work. Because you added an additional tax on one but not the other.

Basically your scenario is:
I can take C from account X or account Y.
X has an additional tax that Y does not have.
Therefore I will take the money from X.
TA-DA!! Y comes out better.

No duh.

Look, all this was hashed out in 1998 when Roth conversions began. There were long threads on TMF discussing the strategies.

BTW, I was on the "conversion is better" side of the argument.
As I recall, Elan was on the side of "doesn't matter."

Eventually it got thorough my thick head that since multiplication is commutative there is no clever way of shuffling things around for the math to NOT be commutative.

You have to look at the entire picture. What happens is that people look at the outside funds used to pay the tax at conversion as "magic money" and don't consider the alternative use you could put it to. The correct alternative to consider is "invest it the same way". The alternative they use, though, is essentially "blow it".

There are still many articles on the internet that argue that conversion is clearly superior. But then again there are lots of people who argue that the Earth is flat.