I think you'll agree that is bollocks. No sane modern invasion plan would consider air supremacy as only a nice to have. In this case we can clearly conclude that other assumptions made at the planning stage were badly, badly wrong.
Russia really fucked up in their assessment of their adversary in all areas. They assumed that a lightning strike would cause near instant capitulation. It wasn't a "blitzkrieg" because the entirety of the world's intelligence ignored the fuff and called it before kick off, publically. Also UKR were able to prepare somewhat.
The horrendous thing about this conflict is that Russia cannot expect to win on their original terms. They will still kill civilians wholesale and destroy infrastructure in a desperate attempt to claim a "win".
Civvies have and will die in greater numbers than soldiers in this conflict and that is something that needs to be considered by us all. At what point do we decide that a possible strategic nuclear escalation is a worse worry than a complete massacre of a sovereign nation?