The U.S. has told Ukraine to keep the Abrams off the front lines, too.

Why on earth have Abrams then, if you can't actually fight a war with them? Are they for show, like the British Challenger? Only good for slaughtering Iraqi insurgents armed with AK-47s and Afghani goat herders armed with sticks?

The Ukrainian soldiers have been suicidally brave, Russia has been casualty-adverse. If Putin was Stalin, he would have declared a war, not just a special military operation, and sent in two million conscripts and Kiev would have fallen in six months. But Putin started the SMO with career soldiers, not conscripts, and they were outnumbered at least two to one, and still Russia has won every major fight with the NATO-armed, NATO-trained, NATO-supported second biggest army in Europe.

As far as adapting, there have been countermeasures, and then counter-counter-measures

Right. But Russia is adapting faster, and better, while NATO weapons and tactics have been failing badly.

Russia has taken about a fifth or more of Ukraine, not including Crimea, with relatively low casualties considering the nature of high-intensity combat in the 21st century. They have smashed something like the first three, or four, mobilized Ukrainian armies, while only needing to rotate their own once so far. They have gained full air superiority. Ukraine has been unable recapture any significant territory, they have only taken back territory Russia voluntarily withdrew from (Russia withdraw from the Kiev region as a good faith gesture for the peace talks in Turkey; they withdrew from Kherson when it became clear they were over-extended (captured too much ground too quickly).

This withdrawal so surprised Ukraine that they thought it was a trap. Zelensky said “It’s important to understand: no one leaves any place just like that” but the Russians did exactly that. The Ukrainians went against a light screening force of national guardsmen and LNR militia, walked into Kherson almost unopposed, and failed to inflict heavy losses on either Russian men or matériel.

Compared to the Ukrainian Army of 2014, which fled Mariupol without a fight when challenged by the half-trained Donbas militia, and only took the city back when Putin pressured the militia to withdraw from the city -- a strategic blunder which many people in the Donbas still consider to be a betrayal -- the modern Ukrainian forces have been brave and tough but even with a two-to-one advantage at the start of the war they never stood a chance.