Though the flat fields are partly why we have neo-trench warfare going on there. There's no cover, so cheap drones dominate the battlespace.
The US was providing air defense systems. Without those the Russian air force will have an easier time operating over Ukraine, but who knows how long Ukraine's current stocks will last. Or the status of Russia's weapons stocks, for that matter.
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.
