Russia shouldn't be worried. Ukraine is corrupt that puts Turkey to shame and their military is below standard, post soviet gear equipped rag tag of a standing army when compared to other countries with mandatory military service.
That was accurate until about 2014. Getting little green men'd + Putin's cronies being sent packing gave them a wake-up call they actually answered to the complete disbelief of everyone. NATO reports gave them two weeks, and jaws hit the floor, including mine, when they turned back Russia's thrust.
Their military got a house cleaning, they seem to have actually listened to the green berets sent to train their troops. The mad-lads went and actually upgraded their military hardware instead of doing the usual slav thing of selling off the upgrade kits. There was a further purging of anyone in command who kind of drug their feet post invasion, fairweather generals looking to see if they could work out a deal for surrendering.
They are still Slavs, fighiting other Slavs, and even more corrupt than you say.
Also, while some generals do believe in the Ukrainian cause, some of them have ordered assaults that make Putin sort of scratch his head and say "Do care even a little about the men under your command?" - but that's any military.
The Western weapons are helping. The foreign bridage is helping. But Ukrainians are still carrying most of the weight.
And they are fighting Russia instead of a competent military, which definitely helps.
The other issue with sending Abrams to Ukraine is the engine. The Abrams engine ain't Grampa Ivan's Soviet truck engine retrofitted for more horsepower and largely unchanged since the 1950s.
The thing is in a league of its own, and is in fact largely unique when it comes to ground based propulsion systems. It's got alot of "fiddly bits" that require its own dedicated mechanics and repair shops. For the US Army, the idea that you need dedicated mechanics and supply chains for the tanks as opposed to everything else is a shoulder shrug. But this is not how the Soviet Army and the current Ukrainian Army function. If an Abrams broke down in Ukraine, they would not be able to repair it.
Never mind keeping it fueled. As you pointed out it needs a particular blend to work.
This is why the US has been pretty free with handing over fancy artillery systems, but not armored or aviation units. Unless there is a dedicated support infrastructure for them already in place the things would be worse then useless. They would be white elephants for the Ukrainian Army.
Having worked with tank doctors... look they can teach anyone with a HS diploma how to fix a tank in a couple months. The bits are fiddly, but as long as you have the bits (and the fiddle) its not like you're doing surgery. They could train Ukrainian mechanics to work on Abrams.
The bigger problem is, as you said, you'd need to send the Tanks AND the bits AND trust slavs to not just walk off with the spare parts.
If this was '24 or '25 Poland could have helped, as they
are working on the rip and replace of their armor to Abrams and I believe its the JP8. But the first deliveries are likely coming too late to make a difference in the current conflict.
