Agree with dying imperial power. But the war was not "pointless". Putin saw an opening. The way out of "dying imperial power" was to reconstitute the former Russian Empire (temporarily known under the name of Soviet Union). Bismark made Germany great by conquest. Germany fought 3 wars during his time (vs Austria, Denmark and France) and won all of them. All of them were instigated by Bismark, none was a defensive war. After these 3 wars, Germany was more than double in population.
If Putin could have conquered Ukraine in a matter of days/weeks, then all the other former Soviet republics would have folded in a matter of a few short years, and with this Russia would have doubled its population.
Putin's big blunder was to not know how inept (and corrupt) his own military was. All the talk about NATO aggression was just a pretext. He was simply hoping to quickly finish the job and present the West a new "fait accompli", just like what he did with Crimea.
We are actually very lucky that Putin let corruption fester inside his military.