You can have the best, most elite fighting force on the face of the planet. They still need weapons, they still need ammo, they still need grenades and rockets and artillery shells, their weapons and tanks and APC's and drones still need servicing and replacements.
In short, Ukraine needs an entire war-oriented production line and logistics/supply system. They have one now, courtesy of the EU, the US, and Ukraine's other allies. A significant percentage of that military aid came from the US. The US is interested in helping Ukraine regain it's full sovereignty including Crimea, and protecting it's European allies. It has absolutely no interest in or appetite for, any real invasion of Russian soil. The US and the EU have repeatedly told Ukraine that Ukraine cannot use any materiel supplied by the US, the EU, or European nations, in any attack on Russia itself.
Ukraine cannot 'win' an invasion of Russia with the weapons it currently has: they don't have enough weapons or anywhere near enough ammo to do it. They may have enough for quick strike forces, but they certainly don't have enough men to actually occupy Russia. Your dream of Ukrainian tanks rolling down Russian highways is just that - a dream.
As for your assertion that "that is not an Army "being supported by" anyone [...] they don't need help": here is a list of military retirement that the US has sent so far - it doesn't even invite what Ukraine has received from other countries or companies. Please explain to me how Ukraine, even with the best army in the world, would win it's war without the weapons and ammo supplied by it's allies. And again, this is just a list of the US military aid, not the EU, not Australia or any of the other countries and companies sending supplies. U.S. security assistance to Ukraine between January 20, 2020, and June 27, 2023:
[Please see my reply to this comment, it's a long list]