Just logistically speaking, imagine needing to send dozens of different types of dozens of spare parts to different sections of a thousand-mile wide front line, with different types, shapes and calibers of ammunition as well. These tanks will likely just be abandoned after they get even slightly damaged.
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Ukraine is “better off” with these Western weapons, but they will be unable to do what they are supposed to do (they’re not too good anyway) due to logistics; hence, the Westerners are giving away very expensive and almost irreplaceable weapons to accomplish nothing. The loss to the West is not justified by Ukraine’s meager gains from this donation.