I dont know what kind of source you provided, but it is clear that those numbers are pure fantasy.
Numbers are from American defense think tanks. Google is your friend!
It's possible that a large part of the numbers listed represent derelict equipment that cannot be refurbished or modernized. But the same caveat applies to Russia.
OK, so huge post-Soviet stockpiles saved Ukraine from defeat
It is the third year of this god awful war, and a very large part of Ukraine's military has never seen a Western weapon.
Most Territorial Defense Brigades and National Guard brigades are fully Soviet equipped. They are fully based on T-64s, MTLB-Us, 152 mm tube artillery, 82 mm mortars, RPG-7s, and AK-74Ms.
Very few brigades have been provided Challengers, Abrams, Leopards, etc. Most continue to fight with the legacy Soviet tanks they inherited, or captured from us.
HIMARS are a rare, and elusive beast. Most artillery battalions are equipped with 2S1 Gvozdika, 2S3 Akatsiya, and BM21 Grad.
The majority of infantry, do not move in Bradley's, or Marders, or CV90s, or Strykers, but in BMPs and MTLBs. Many move on SUVs provided by volunteers.
The lion's share of Russian drones and missiles are shot down by Soviet era SAMs. Only Kiev, Dnipro, and Odessa are protected largely by Western systems.
Ukraine is still fighting more on its Soviet stockpiles than on NATO aid. This is why when aid does come from the West, the most important aid is usually from Bulgaria, Poland, and Czechia - that themselves have large Soviet stockpiles.