First of all, the "we're only sending old, decommissioned gear" is utter rubbish. Over half the US aid to Ukraine is in the form of direct cash payments, and US military contractors are working overtime to craft brand-new munitions and weapon systems, as well as depleting our own reserves drastically.
Furthermore, the "we're weakening Russia" hype is nonsense as well. Russia's active military count today is 1.5M troops, up from 1.02M before the war, and -- for the first time in 30 years -- Russia is drastically increasing its military budget, rather than the slow decline its seen since the fall of the USSR.
Even more importantly, the Russian military in 2020 had never fought a modern war. Today, they have solid experience in fighting against US military tactics -- those we've been teaching Ukraine in joint war exercises since 2014 -- as well as priceless data on the actual capabilities of the US's latest military weapon systems.
Finally, all of this is moot in the final analysis. Russia has 2,000 tactical and op-tac nuclear weapons, and a total nuclear arsenal exceeding 7,000 warheads -- more than all the rest of the world combined. Despite what the unicorn-and-rainbow crowd believes, Russia can and will use them to defend Russian territory. And the primary purpose of annexing Donetsk and Luhansk -- which Putin long resisted throughout the decade-long Ukrainian civil war -- was to make the use of such weapons in Ukraine legal under the Russian constitution.