Yes, it’s most likely that since as far as I know and have been told by Cloudflare’s Team (there is a post somewhere in this thread about this by @cscharff) all plan levels have access to all POPs (except China) on a general basis. There could be instances, but those are temporary are really rare, where for reasons a POP might be limited to high tier plans (Enterprise has priority, then Business, Pro and Free).
ISPs can decide what to do with packets they receive, so if the cheaper (or less congested route) for them is sending all traffic to Tokyo for Cloudflare’s IP ranges they can and most likely will do so. This is usually solved with direct peering, but - assuming this (https://blog.Cloudflare.com/bandwidth-costs-around-the-world/) is still valid, which I expect to be, even if to a lesser extent - are rare to set-up and have with the ISPs down under.
I unfortunately have only two solutions, both of which won’t be ideal, but unless you can get the ISPs to fix it (and I doubt in the short term) we are here.
Stay on Cloudflare, but move the AWS infrastructure closer to the actual POP from Cloudflare (ie. Tokyo), it would prevent double roundtrips for most traffic while most likely improving worldwide latency (Australia is a bit far from everything else). This basically halves the latency, while retaining caching and protections from Cloudflare, Argo won’t really help much then since the improved part is Cloudflare’s POP <-> Origin. In this case you could probably think if maybe moving some of the infrastructure to Workers could help (reduce latency, still from Tokyo unfortunately, costs and improve availability).
Leave Cloudflare moving everything to AWS. It would increase costs (higher bandwidth for sure, most likely additional server capacity), but definitely lower latency to Australia. In this case ISPs don’t have the option to direct traffic off of Australia since that’s the only place the content is. It would have no DDoS protection, no WAF, no caching and no improvements on the worldwide market, but it depends on the target audience.
Unfortunately I don’t really see a good answer unfortunately, but Cloudflare can’t do anything. I am in some ways in the same boat as you where my ISP prefers a POP 3x times farther (latency wise) than the closest one. Luckily it’s only a handful of milliseconds in my case.