So which controllers are you talking about here then....?
Yes. So capable and professional that they can't mix IFR and VFR traffic where VFR does not affect IFR
You must be talking about controllers who have the option of permitting IFR and VFR to mix, but choose not to. I'm sure you're not referring to controllers who work airspace where VFR flight is not permitted, as that would be a rather spurious argument.