It is ironic that a large portion of the weapons that are now being sent to help Ukraine defend itself are old Soviet era equipment that was left in the various satellite states when the Soviet Union collapsed. Czechia has already sent some T-72 tanks, and Poland has announced that they have hundreds of those that are in good condition but not in active service.
These are old weapons, but they are of the same type that the Ukrainian army already has, meaning that they can be deployed very quickly. Russian troops have access to more modern tanks, but many were lost in their failed battle to take Kyiv. The reserves are older systems, mainly variants of the T-72. Some of those are in fact older than the ones that are now sent to Ukraine, because at the fall of the Soviet Union, their most modern tanks were deployed in countries close to the Iron Curtain rather than in Russia proper.
Thus, the Soviet aggression in placing armed forces in forward positions in countries that used to be under their control now comes back to bite Vladimir Putin when he tries to return to the old times of Soviet domination over Eastern Europe. Time has passed Russia by, and there is no longer any way back.
Thankfully.