I suggest you look up the judgment from the Navair Bankstown mid air.
The ATCs where given 30% of the blame because the judge said ATC could see the two aircraft and therefore had a duty of care.
For a decade after, ATC separated VFR from VFR to IFR standards in Sydney.
I would have to orbit at Hornsby for ten minutes while they separated my helicopter from the channel ten chopper with IFR standards!
Well it certainly doesn't work like that anymore!! IFR are given traffic on known VFR, same as VFR to VFR. It's up to the PIC to ensure their own separation, which is then the Achilles heal of Class E airspace. In reality Class E is Controlled Class G. Ultimately the PIC is still responsible for VFR separation. Too bad for you if you are in the outback and wipe out someone on descent who is not "known".
It only takes one instance of avoidance action by a IFR aircraft to totally unravel Class E. They have to avoid a VFR aircraft, this means taking action, yet they need a clearance to take action so then a 4+ way radio conference has to take place, between the VFR traffic, other VFR traffic, the IFR traffic and ATC.
In reality Class G is safer and easier to operate in as everyone knows where they stand. Class E only really works if everyone is identified and ATC can actually give avoidance guidance. The current arrangement where jets are cleared through overlying Class E and have to self separate from VFR traffic is a nonsense at the speeds they operate at with no radar coverage.