Never underestimate rasputitsa either... https://en.wikipedia.org/wiki/Rasputitsa

S-300 were better air defence systems. Sure others can help also, but at the end their supply is limited. On the other hand Russia has thousands of fab bombs and is easy for them to make the glide system. Lancet drones are easy enough also. So, Ukranian air defense will be overwhelmed no matter what... They have a chance to do the same to the Russian air defenses though. They have done it already several times, even if it is more difficult.