If Russia has poor air defences and a cowardly air force then this should limit their combat effectiveness.
And it does. There's a reason Moscow couldn't take Kyiv in the first push. There's a reason the VDV and the 1GTA were rendered combat-ineffective. There's a reason Moscow has been reduced to Zeno's advance.
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Not that it matters to The Don or his arguments, but you can still see the janky, disjointed remnants of Soviet doctrine in Moscow's prosecution of this war.
The Soviet Union never expected to achieve air superiority over NATO. Thus their doctrine evolved accordingly. Their air force would be strong enough to deny air superiority to NATO. This, in conjunction with heavy air defense systems on the ground, would greatly blunt NATO air power. This, in turn, would give Soviet artillery room to work. This would create the conditions for the Red Army to launch attacks all up and down the line, with large numbers of inferior troops and equipment. And this, in turn, would create breakthroughs that could be exploited by the "elite" units.
And we see that against Ukraine, which has even less air power than Moscow, the basic prinicple is sound. But Moscow is faltering, because it no longer has the necessary numbers of inferior troops, nor the requisite well-trained and well-equipped "elite" formations, to properly finish the job. What we're seeing now is that even under the Red Army's doctrinally optimal air power conditions, Moscow can only produce a sad parody of Soviet deep battle doctrine. Their artillery is too weak and uncoordinated. The battalion task groups falter. The "elite" formations are simply not there.
That's what NATO would be facing, today, if their air power were degraded to Ukraine's current level. And today, even without air superiority, NATO would eat this Russian army in Ukraine for lunch. But we already know, from Desert Storm, that even at its peak the Soviet air defense system was powerless to deny NATO control of the skies.
So if the conversation is about what this war in Ukraine can tell us about NATO's chances, then the answer is, NATO would have wrecked the RAF on D-Day. Three days to Kyiv? More like three days to Moscow. Indeed, if Ukraine had had just a couple more years to prepare, they could probably have achieved the same result with a fraction of NATO's power. Which is probably why Putin rushed things.