The US does conventional warfare more effectively at all levels.
The US did not lose in Vietnam, Afghanistan, or Iraq. It never lost any major battles in any of these wars - it won 90% of the battles it fought. It never lost or gave up ground in any of these wars. It lost fewer troops than the enemy in all 3 wars. US politics and public opinion forced the US to leave all 3 countries. Also, in 2001, when the Taliban were weak and ready to surrender in Afghanistan, the US passed on a deal.
So, it is the weapons in Ukraine that are beating the Russians?
Russia was listed as the 2nd most powerful military in the world until the Ukrainian conflict. Like you said, NATO trained forces (civilians) in Ukraine are beating the Russian Army. The Russians didn't face their opponent more effectively in Chechnya, Georgia, or Syria. They just killed a lot of innocent civilians instead. A shit-ton of civilians. Russian soldiers rarely engaged the armed enemy - they are cowards. Unlike their Soviet counterpart in WWII.