This is actually a much better tactic than head long assaults into well fortified positions that are murder zones for Ukraine recruits.
Make the ruskies defend THEIR territory for once.
If course this could backfire as Lees’s incursion at Gettysburg.
Time will tell
Don't worry, they will. Russia has a pretty good track record. How many troops does Ukraine have?
"Operation Barbarossa, the German invasion of the Soviet Union on June 22, 1941, involved over 3.5 million German troops and nearly 700,000 German-allied troops. "
Actually, you could argue that Ukraine could go into Belarus and liberate the country from the occupiers. The Russians invaded Ukraine by using Belarusian territory so it's fair game.