Neither has anyone else. There hasn’t been a major land war between technologically advanced, well matched opponents on a large scale since the 1980s (Arab-Israeli war in Lebanon-Syria). The Russians certainly haven’t faced anything like the Ukrainians, and they still overmatch them in many areas. And the US has vast resources, in tech and numbers, beyond what the Ukrainians have access to.
Time will tell who is right. Still, in a war of attrition, Russia will win. Americans suffer with Bodybagaphobia. We lose 5,000 men in Iraq and its terrible. Ukraine has lost 100,000, and they keep fighting. Russia too has lost a lot but they don’t blink—what will happen if we get involved and stray to lose say 20,000 KIA? What will that do on the home front? War is bad but some war hawks want it.