This is just one fatal assumption that western had on Russia: they don’t know how to innovate and adapt to modern warfare. In fact it gave the western such impression only because it was not in a serious war for a long time.
But they do have the advantage of greater manpower and enormous equipment stockpiles, which compensates for a multitude of errors.
Russia has taken (by the most conservative estimates) on the order of 10x both killed and wounded as the Soviet Union itself took in the nearly decade-long war in Afghanistan which was a major contribution to the collapse of the USSR in a little over two years.
That Russia took almost 3 years and a presumed 300-500k casualties to begin deploying basic air support with guided glide bombs, like the west has been doing for 25 years, was indeed surprising.
Every military has the ability to innovate and adapt because the life of every member of the military is on the line each day. It took an astounding number of embarrassments and lives lost for the Russian military to adapt, including a near coup by PMC Wagner.
Just to point out FAB-500 glider bomb use was already recorded in March 2023, so it took Russian a year not 3 year, so your perception is factually wrong.
BTW, to emphasize the low starting status of Russian military at the beginning of the war does not defend our mistake either, rather it reinforces that argument.