They may have not lost a large number, but having them and being mission capable and proficient pilots to fly them might is another
They are putting huge numbers of hours on their air frames and just a guess but imagine their maintenance is not 1st world either
“They are putting huge numbers of hours on their air frames”
Good point. I think that is true. Even though many types of Russian aircraft (fighters and bombers) are mostly staying out of Ukrainian airspace where they might be shot down, they are operating a lot more; patrolling, feinting and launching long range weapons.