If you do 100% UK air, until UK4-5 you’ll do better than if you had started with a UK1 fleet build.
What I anticipate should happen after that? History of game as I anticipate it - Germany controls Africa, you kill the German Med fleet, Germany builds subs at Med to protect Africa from US landing, maintaining control of Norway (which is usually lost very early on). Japan presses forward with transports/ICs. UK/Russia hold up at West Russia pretty well, but once Japan hits Novosibirsk/Kazakh around J4-5, Russia’s forced to bleed off strength east to keep the Japs at bay, which means Allies have to retreat from West Russia; losing control of Africa and Norway is not good, but not fatal - being forced to huddle at Moscow with only UK fighters to reinforce, though, should be the beginning of the end for Russia. Germany or Japan grabs Caucasus; Russia may be able to reclaim at heavy cost, but with nothing to stop the steady flow of Axis reinforcements, Caucasus falls, then Russia.
US can divert to Brazil before hitting Africa, but that means diverting transport escorts and transports for additional turns, which Russia may not have with all the Axis pressure.
You could definitely do UK fighters/Russian infantry to stave off Germany for a long time, but Japan, Africa, and Norway are what make the real difference. If US goes against Japan, Japan is slowed in Asia, but Germany producing cost effective ground units powered with additional Norway and Africa income, combined with just a BIT of pressure from Japan is enough to make things very difficult for Russia. If US goes in the Atlantic and helps Africa, Japan runs free in Pacific and pressures Moscow directly.