All that shows is that, theoretically, one can come up with a system in which generational GC is counterproductive despite a high infant mortality rate. That is not an argument that generational GC is a bad idea in practice, and the article is clear not to make that argument.
Comments
You might find Baker's thoughts on Generational GC interesting[1].
[1]: http://home.pipeline.com/~hbaker1/YoungGen.html
All that shows is that, theoretically, one can come up with a system in which generational GC is counterproductive despite a high infant mortality rate. That is not an argument that generational GC is a bad idea in practice, and the article is clear not to make that argument.