The game changer was the FAB bombs. They can take out a building in one shot. The same building would take a week for artillery to demolish. The FAB and Russia’s advantage in artillery and manpower are too much for a fading Ukrainian military.
The Russian Army learns slowly but it does learn and they do not give up easily. The Russian military is now battle tested and has ramped up its doctrine, tactics and technology to the point that I believe it is the strongest military on land. Aside from its nuclear submarine fleet the Russian navy really isn’t a factor.
One thing you never hear mentioned is that if NATO and America join the war against Russia then China will then enter the war. There is no way that China will permit a western dominated Russia increasing their encirclement. If there’s one thing China has plenty of, it is young men, money and munitions.