Thumpalumpacus
Major
The Russians are in a much better manpower position, enjoying a >4:1 advantage over Ukraine pre-war population of ~40million. And since the war began Ukraine has lost somewhere between 7-10 million to outwards migration. If this is a war of attrition, which by all appearances it is, then Ukraine is in a very disadvantageous position.
The problem with Russia's manpower is that they're woefully trained and equipped.
You say the supply and equipment issues are neutral at worst but I see no way for that to be true. Russia has a large domestic arms industry that is producing its munitions, repairing its tanks, ect. Ukraine has a much smaller arms industry that relies on imports of shells, bullets and all matter of war material. They have to send many of their tanks and artillery pieces to Poland for repair. And they are reliant on fuel imports as well.
Uralvagon has greatly reduced its AFV output, and largely given its workforce the task of repairing damaged units.
The Kremlin Wants "Uralvagonzavod" to Repair Tanks 24/7 But There Are Not Enough Workers | Defense Express
Therefore, it is necessary to put either pensioners or generally untrained people behind the machines
en.defence-ua.com
Furthermore Ukraine is dealing with very serious disruptions to its rail and electrical grid which place further difficulties on supplying the front, by comparison the Russian trains are still running, they have no power issues, ect.
Even with all those trains running, the Russians can't seem to get their logistics in order.