Main problem of Russian military is logistics. Food is sometimes outdated, fuel is rare and they need a lot of ammunition. Modern systems are more rare than anticipated. Armata 14 is for example hard to be seen. Austrian military analyzer told, that Russia is much more dependend on trains, as any other army. This makes them vulnerable for partizan attacks. Ukraine soldiers know, how to perform that (They already did it agenst German Reichswehr in WWII). Without fuel even the most advanced tank is only a piece of metal.