So I am using Woolworths mobile which "uses parts of the Telstra network" ie. their wholesale network.
Does Vaya/Amaysim/Yomojo/etc only use part of the Optus network too?
I'm aware Virgin has a relationship with Optus akin to how Boost Mobile is related to Telstra.
Is the Telstra wholesale network still superior to coverage offered by Optus and Vodafone MVNOs, or is it comparable?
AFAIK all Optus MVNOs get access to the entire Optus network. If you read Amaysim's IPO prospectus they talk about their Master Services Agreement with Optus and the crux of it is that everything Optus has Amaysim gets to use, including no differentiation in priority of customers (i.e. Amaysim customers must have the same priority as Optus' own customers).
Network coverage and performance depends heavily on your location.
This is one of those topics that people can argue about endlessly, yet almost no one can speak a "universal truth" since coverage varies so much across the country, also varies depending on the handset (carriers use diff frequencies in diff areas, particularly for 4G), and even local factors like outages and maintenance.
Purely as an example, I live in Sydney and frequent the city and about 20km north/north west of the city. My coverage and speed on Optus 4G was without fault but last month I switched to MeU which uses Telstra 3G only and I regularly find black spots where I have zero signal, or I have signal but no data. But I suspect this is due to MeU being 3G only, I'm pretty sure if I had Telstra 4G as well there would be no problem.
IME Telstra, Optus and Vodafone are all roughly equivalent within Sydney. There will be specific locations where one carrier is better or worse but on average its all much of a muchness. I'm using a phone that supports all frequencies from all carriers.