As a Ukrainian at war since day 1 – I don't buy it. They will sell their gas at discount to China until the very end. Military force is the only way to get them to the death zone.
As someone with no firsthand knowledge at all, I am inclined to believe your position is correct. But I also think the Economist is making an important point: Russia's continued prosecution of this war will shred their internal economy with consequences lasting for decades or centuries. What people often underestimate is just how much damage an economy can suffer before breaking down entirely. But Putin doesn't care…
It's not clear how the Russian army will improve when the economy declines.