The document you posted quotes the S-211 has having a reduced risk as a small aircraft. You're quoting a document that is referring to aircraft like MIG-23's and F-4's with engine driven hydraulic powered flight controls that can not be controlled in the event of an engine failure and that are substantially heavier and more complex and trying to apply it to a light trainer jet with no powered flight controls that was fully controllable.
The AWAL permit index system applies restrictions to warbird aircraft based on their complexity, known history and risk factor. The S211, like the L-39, has no overflight restrictions and more often than not are Permit Index 0 (no limitations). Perhaps you should read up on limited category aircraft in Australia. Your assumption that warbirds have not been regulated here or aren't risk managed is absurd.
https://www.casa.gov.au/aircraft/spo...Relatedcontent