The Ukrainian statement does not address the claim at all. Saying their forces are continuing to fight does not challenge or prove wrong the statement of 80% plus of territory being Russian held. It’s an obfuscation. Plain and simple.
The only fact I can take away from the Ukrainian statement is forces are present in what ever remains and they continue to fight.
However, I’ve also heard reports that many Ukrainian soldiers are surrendering. That I don’t doubt. The situation appears so dire that surrendering is likely the smartest move and best chance of surviving.