Well Russia hasn’t managed to destroy Ukraine’s existing manufacturing capacity

they have though

Minister of Strategic Industries Kamyshin claimed a twenty-fold increase in artillery shell production over 2023 a couple of months ago

they can claim whatever they want for propaganda, in the real world we can observe their artillery shortages and failed offensives

despite Ukraine’s lack of a real airforce, has not been able to successfully establish air superiority

you don't need air superiority to destroy a factory, please put aside the wishful thinking for 5 minutes if you can

troops can retreat, equipment can be relocated somewhere else, a factory is a static building that you CANNOT MOVE, no matter how much air defense you put near it eventually a missile, drone or shell will go through and damage/destroy it