It's hard to say whether modern warfare favours defence over attack, as much depends on the belligerents, but it is fair to say that the days where you could simply overwhelm defences with cannon fodder and sheer numbers are long gone.
A quick google search says that the Russian army is a million strong, with another two millions reserves. But they won't all be soldiers; and of those who are, a fair chunk will be conscripts rather than professional soldiers.
Oryx puts Russia's MBT losses alone at more than 670 confirmed kills.
https://www.oryxspioenkop.com/2022/02/attack-on-europe-documenting-equipment.htmlI don't know how reliable this information is but they claim to use photographic and video evidence to determine losses. If accurate, then surely those are unsustainable losses?
Based on that, the conclusion is that Russia is incapable of fighting a multi-front conventional war. Every other nation that might be considered a target knows they're a potential target; by the time Russia can turn it's attention to the Baltics, or Finland, or Poland or wherever else, they'll all be ready for them.