I am not as optimistic as you, but this the 12 day and the season of mud approaches... in 9 days it should arrive and if Russia has not taken Kiev by then, the Russian supply situation should worsen.
After looking at some rather detailed videos it is clearer to me why the Russians have had difficulties. In short:
-They inserted paratroopers deep into Ukraine, only to have them surrounded and often eliminated.
-They failed to knockout the air force.
-They failed to prevent easy movement of Ukrainian forces.
-They had poor coordination between top cover fighters and ground attack aircraft.
-They failed to knock out communications, or command and control.
-They weren't prepared, plans were slapped together, commanders didn't even know of the offensive till the order was issued to cross the border. Maps were not provided, channels are for radio are unencrypted, etc.
-Ukrainians do not concentrate forces till needed, keeping them dispersed to lessen chances of being destroyed by artillery or air.
-Ukrainians learned all the Russian tricks from their years of conflict in the eastern Ukraine.
-Ukrainians have their own tricks, such as cheap domestic produced drones with bombs...kamakasie's if you will.
The most egregious problem, however, is Russia's military structure. Because roads are problematical in much of Russia, the army is built around rail transport. The theory, for self defense, makes sense. Lots of rail lines in Russia, and railroad repair battalions attached to units. However, Russians have many fewer trucks, and fewer fuel trucks, than US military. Moreover, while the west uses 'pull' supply (units order what they need) Russians use 'push' supply (top command decides what units need and don't need, and it is sent to all regardless of their needs).
They dispatched convoy, four abreast, shoulder to shoulder with no return lane. Because of the low number of trucks, maximum distance from a railhead is less than 90 miles (or Km, not sure). Ukrainians have blown their own rail lines and bridges. And Ukrainians have made fuel trucks their priority target.
It's worked. Russians have tried disguising fuel trucks, Ukrainians quickly caught on and used social media to distribute instructions and photos on how to detect them. Worse yet, going off road even now is very difficult because of mud...exacerbated by intentionally flooded fields (and the Russian destruction of a dam...kinda stupid, eh?)
Limited on food, fuel, and ammo...lead units of the convoy have been checked, and the line repeatedly attacked along its length.