being big land is actually a negative when air force coming into play, many areas where a jet bomber can slip and drop a bomb on a high value target. china has many bridges and dams where if they got destroyed 25% of their land could be flooded and large rural populations completely destroyed and land becoming inaccessible. chang kaisheks army during the chinese civil war after ww2 demolished many bridges and dams near the communist insurgency and did enough damage that for some time he was winning (him losing was due to the backlash of doing something like that but in a us/china war this is irrelevant).  russia can't cover their whole territory with aa systems and they just barely now can cover the whole ukraine border so any attack from the far east by long range bombers would require a lot of aa to cover strategic assets (like maybe 2x of their current number).  this all would require a huge effort by the us air force that if done correctly enough (decisive is not necessary) would win a war in 6-7 months time. if not done in that time frame then yea the us would not be able to cope long term.
Greece