I am sure they have done analysis. Every Russian Mi-8 has either 2 or 4 external fuel tanks. so assumption is there speed is slower.
just look at what Ukraine medic is facing due enhance capability of drones. The point is this highly distributed conflict. Even mis firing of Air defense missiles. when system is overloaded can create alot of damage. The reliability of missiles and launcher 24/7 becomes very important. or Russia own cruise missiles can hit civilians as they are normally fired from several hundreds km.
Ukraine is not even 10% of Russia airpower because this glide bombs are limited to Su-34 sorties and with not full load out. Shoigu said Su-34 is doing 6 sorties per day on average and that was nearly two years ago. Now Su-34 fleet is way larger and range of bombs 130 to 400km. The greater the range the less time for sortie. now take this template against peer competitor with the intensity of missile launches, air defense and glide bombs much higher and same on receiving end. This need much larger and more capable helicopter fleet.