You are using some very poor sources if they have given you the idea that Russia has 20 million soldiers to mobilize. Russia is facing a severe shortage of manpower too, made worse by the fact that they rely on constant costly attacks by small groups of infantry that have very short lifespans, whereas Ukraine is increasingly automating the war and relying on unmanned weapons more and more. For example, Ukraine reached parity in drone strikes in early 2026 and is now carrying out more drone strikes than Russia. It's increasingly rare for Russian soldiers to meet any Ukrainians before they die; about 80% Russians die by drones as drones have become significantly more lethal. In 2024, drones killed about 1/3 of soldiers on impact. Now they kill about 2/3 of them.
Also, the "slow but steady advances" are a complete Pyrrhic victory if you look at the numbers. Russia has gained less than 1000 sq km this year at a cost of at least 100 000 lives. Ukraine is over 600 000 sq km in size. The daily number of casualties hit a new record a few days ago, exceeding 2000, about half of which are deaths. Russia has no hope reaching the territorial control it had 30 days into the war, let alone anything beyond that. It is by all objective measures one of the worst military disasters in the entire Russian history.