Creampuff, I'm sure there will be some controllers on here who control in non-radar airspace that would be able to give you a fairer reflection and more accurate picture, as to the effect in my radar airspace (in the ADSB exempt airspace on te J curve) of an aircraft not having ADSB at high levels is none...(presuming they have working transponder lol) as we can utilise 5nm lateral or 1000ft/2000ft vertical separation between any mix of ADSB & standard transponders
More of a problem are the slow & normally non-RVSM aircraft going into those levels (like some Citations ) but RVSM is a different topic
But we let them up there because we have discretion to do so and normally the workload allows us to manage it & not hinder RVSM approved aircraft.