We are not sending our frontline stuff. We are sending equipment that is scheduled to be decommissioned and scrapped. 2nd, our equipment is designed to fight in the US style of fighting, which among other things requires air superiority. Ukraine doesn't have that.
Lastly, look at numbers. Look how many Russian tanks have been destroyed vs Ukrainian, Russian planes vs Ukrainian, Russian casualties vs Ukrainian. Our strategy has been since 1941 "steel not flesh". We expect steel losses to preserve human life. Looking at Russian casualties, they use flesh and not steel.