By your own example, both ways come up with the same result - a two name species or botanical name. Why quibble over whether the second name is called species (nice short word) or specific epithet? It seems fairly common usage to break it down using the terms genus species cultivar.

What do you mean? Let me explain one more time:

Genus

Everyone agrees that the first word of any scientific name is called the genus.

Species

I define the word species as having only one application. The species is the same as the scientific name, meaning the genus and the specific epithet combined.

This is a species in my opinion: Hoya australis

The NGA defines the word species as the second part of the scientific name.

But what is the scientific name referred to in the NGA? The species too or just the scientific name? If the NGA thinks that the word species has two applications then that's confusing!

Anyway I really don't care of what people want to call the second word of the scientific name. Experts disagree, and so there's no real answer to who is correct.

What I really want to know is whether Hoya australis as a whole is also considered a species or whether it's considered a botanical name/scientific name.

The admins here are well aware that, in your example above, Hoya is the name of the genus, australis is the specific epithet, and the scientific name of the species in question is Hoya australis.

The "Add a plant" page uses the term "species" rather than "specific epithet" for one simple reason, it's an attempt to minimize confusion. The average person has no idea what the term specific epithet means. Many people struggle to properly fill out the boxes in the "Add a plant" page as it is, without additional technical jargon.

In your case, we appear to have created confusion by the use of less than precise language. But, there's almost always a trade off between precision and usability, and I'm fairly certain that the use of "species" rather than "specific epithet" has prevented more consternation on the part of members than it has created.

Thanks, @kentpfeiffer! You finally answered my original question.