US reports are worthless, because it has no soldiers on the ground.
The extremely high Russian casualty rate has been reported by multiple independent sources from inside Russia.
For instance:
> "Everyone went to the SVO," Astashov told RFE/RL, using the acronym for "special military operation," the euphemism the Kremlin has insisted on using when discussing the war in Ukraine.
> According to Astashov, the size of the brigade when it deployed was about 1,500 troops. The total number of dead, by Astashov's estimate: "At least several hundred."
https://www.rferl.org/a/russia-army-casualty-rate-64th-briga...
Also, many huge Russian loses in Ukraine were confirmed by NATO countries with visuals:
> The British defense ministry on Friday said satellite imagery has confirmed that Ukrainian forces decimated a Russian battalion as it tried to cross a series of pontoon bridges over a river in northeast Ukraine earlier this week, a dramatic setback for Russian forces already struggling to make significant progress along the eastern front.
> Russian battalion groups generally have between 700 and 1,000 men.
https://www.nytimes.com/2022/05/13/world/europe/ukraine-russ...