I don't know that russia has air superiority over the entire country, or even over the area that they control. MANPADs and stingers have been pretty effective in at least creating a sense of continuing chaos.
People focus on the helicopters where those pose a significant risk. Ukraine is not flying because Russia has air superiority. Air superiority simply means they control access to the skies. Russia absolutely does have that. The fact that manpads can pose a risk to aircraft doesn't change this.
Ukraine also has a few aircraft (less than 100) and just a handful of helicopters. Thus in just numbers alone, the Ukraine is not going to be able to field any sizable presence. It's better to just let the russians fly and shoot anything in the air with stingers.
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