Sorry, but this sounds like copium. How much land Russia gains per year? How much money in taxes can be raised from bombed ruins with zero infrastructure, no population and economic activity? Russian budget deficit for 2026 is projected to be at 6 trillion roubles now, more than 1.5x higher than the 3.8 trillion deficit that was estimated during planning.
As was already mentioned, Russia faces the challenge of maintaining a stable economy under massive sanctions and prosecuting a war. We can see the thinking of the Russian elite when they called the invasion a "Special Military Operation" - a precise usage of military force to accomplish a political goal. They
thought that the Ukrainians would come to the negotiating table and that both sides would hatch out a solution, albeit one in Moscow's favor.
They did not expect Ukraine to wage total war, effectively destroying its demographic and industrial base, whilst being funded by NATO. The combination of devastating sanctions and a war that they did not comprehend in its entirety (who could), forced them to recalculate.
On the economic front, contrary to proclamations of collapse, they have faired really well given the circumstances. The elites were forced to invest in their own economy and shift their business outlook eastwards.
On the military front, they have to get through industrial fortresses laden with underground networks and bunkers, manned by men (and increasingly women) who are paid by Brussels. Ukraine does not face the same economic constraints that Russia or any other country would when fighting a war, in the sense that their only job is to worry about the military. Russia can try to break through these fortresses by massively ramping up the army, but would face economic constraints and Ukraine could enlist its last brackets of men in response.
So they've decided to play it slow, conserving casualties and economic stress. The war would probably end when the AfD come to power in Germany + Reform in the UK + Le Pen in France. Of course it could end earlier than this, and we can see the Europeans attempting to make connections to Moscow. The combination of a rapidly declining industrial base + a weakening Ukr (see youth conscription debate) + America removing forces in Europe will be factors in ending the war. Or Ukraine could just collapse.
For other countries looking to get fight wars in the 21st century, blitzkrieg will be an attractive option, given the Ukraine example. The US tried to do some stupid form of this by relying on airpower and the brains of octogenarians so it doesn't count.