"Russian troops have been fighting in Ukraine for more than four years. That is longer than Soviet forces fought in World War II" [four years]
The explicit comparison to WWII duration, combined with the article's note that Russia still hasn't taken the full Donbas, directly evidences military overextension against stated objectives.
Reasoning from this article
The article layers three compounding signals of overextension: campaign duration exceeding the historical precedent invoked for legitimacy, failure to achieve the primary territorial objective (full Donbas), and drain on a $3 trillion economy. This generalizes to a structural dynamic where attritional wars between a large power and a smaller but externally supported adversary tend to produce stalemate lines rather than decisive outcomes, while the larger power absorbs disproportionate economic and reputational costs. The scaled-back Victory Day parade is a visible domestic symptom of this structural strain.