"arming Ukraine to the teeth" does not guarantee the victory but guarantees more casualties and suffering. To win you also need to have 3x more soldiers which is not the case. West cannot even pay a salary comparable to what Russia pays to its volunteer soldiers.
We can both agree that arming Ukraine with more missiles will guarantee more casualties and suffering... for the Russians.
And in response, Russia will do what exactly? Send more golf cart brigades or more North Koreans? It's not like Russia has enormous military resources they've been keeping as a surprise. No, if Russia could do anything differently they would already be doing it to win the 'Special Military Operation'.
Draft more soldiers, for example. Missiles falling on Russian cities will increase motivation to go defend the country and will make a good cause for involuntary conscription.
If the Tsar does resort to involuntary conscription, I hope there are some Ukrainian drones around because we'll get to see the next Great Russian Revolution in 4k!