I understand why you’re frustrated; Germany does start off very powerful in Global 1940, and that’s why the Allies usually need a bid of some kind, especially in beginner-to-intermediate levels of play.
If you’re doing Taranto properly, you should also be picking off the lightly defended Italian transport near Malta on UK1, which means that the Italians start the game with only one transport. They can’t attack both Morocco and Gibraltar with the same transport, so your fighters should have a guaranteed return route to London after a successful Taranto raid.
Also, if German is attacking both your Canadian transport and your Welsh transport, then they should not have enough subs left to knock out both of the main British Atlantic fleets (Channel and North Sea) without major casualties in the air. Depending on what Germany built on G1, you may be able to consolidate what’s left of the British warships, build a carrier and a pair of destroyers in the North Sea on UK2, land the French fighter on the new carrier, and then flat-out block the G3 attack on Scotland by denying Germany control of the sea zone.
Part of the trick in defending against a Sea Lion is to wear out the German Air Force one step at a time. Like, the Luftwaffe will take casualties sinking the original British Navy. Great. Then make them take even more casualties sinking the new British Navy that you rebuild. Then make them take casualties occupying London. At that point they should be down to one or two planes, tops, which makes it much easier for the USA to build up forces near London and for the Russians to trade at an advantage on the eastern front.
Finally, a G4 take of London does not lead to the Germans “pushing back” against the Russians on G6. They put units in Berlin and Hanover on G5, and then those units could theoretically reach Poland on G6, but that’s still only 20 German units, and the Russians have had time to build about 12 * 3 = 36 Russian units on R1, R2, and R3 that have already reached the front lines, plus Russian starting forces outnumber German starting forces once Germany moves 14 transport loads from mainland Europe to the UK. Germany doesn’t have the strength to attack the Russian stack in Poland on G6.