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The theory raises questions.

What was the sequence of progression from no-sperm critters to virile critters?

You’ve got a whole hardware store of parts to assemble in order to have a functioning sperm-producing animal. There are nerves, hormones, sperm-making cells, genes, not to mention the body and swimmer tail of the sperm itself, along with the built-in understanding that they have a destination and function.

Then you’ve got the whole mechanism to deliver the sperm, the tubing, blood supply, stimulant mechanism, and the ejaculatory musculature.

Then, in the same generational sequence and locale, you’ve got to explain how the female system showed up on the scene with all of its hormones, tubing, sperm-receiving hardware, nerves, ovaries, eggs, genes, blood supply, and the knowledge to use the package in concert with the male.

And then you’ve got to get the boys and girls working fast to do this because you’ve got one generation to get this done before the species dies off.

They’ll need Barry White to set the mood.

This is why my copy of The Blind Watchmaker is all scribbled with margin notes. Evolutionary theory sure is fun.

It depends on what the said organism was like, 600 million years ago. One cannot assume that the sperm cell did not change during the time from then to now - thus affecting the assumptions regarding what sort of delivery mechanisms and support structures might have been required to enable its function, initially.

For example, female bed bugs are impregnated by male bed bugs injecting sperm directly into the female’s bodies, by puncturing its physical integrity.

What was the sequence of progression from no-sperm critters to virile critters?

See my preceeding to CTOCS.

Then you’ve got the whole mechanism to deliver the sperm, the tubing, blood supply, stimulant mechanism, and the ejaculatory musculature.

Then, in the same generational sequence and locale, you’ve got to explain how the female system showed up on the scene with all of its hormones, tubing, sperm-receiving hardware, nerves, ovaries, eggs, genes, blood supply, and the knowledge to use the package in concert with the male.

See also my preceding. None of these changes need to have been concomitant. These would have been very simple animals, maybe even pre-animals. The only thing that happened, at first, was that they went from releasing undifferentiated gametes to releasing dimorphic gametes. This initial innovation allowed many other innovation to follow.

But, really, even this was just a new way of doing what had been done before, even by singled celled eukaryotes. At least I think it's the case (although I'm no expert) that some protists create haploid cells which are sexually "typed" in some fashion that they can only fuse with opposite types. In practice the same as eggs and sperm, although it's a different mechanism.