Ok, Iam going to start this from going in reverse order based on GHG video.
Why it is a total waste of time building 2 Air Bases to defend SZ110?
Now the idea of defending SZ110 is to prevent the USA or UK from coming into that zone to contest the conquest of London. Deny them a immediate response and give Germany 1-2 turns to build units on London to hold it.
The bottom line is the bigger picture of the war. The Europe map is really a struggle between Germany and Russia. For Germany to achieve a global victory on the Europe map they MUST take out Russia. UK/USA are the spoilers in this big picture plan. They are trying to distract Germany and attacking them in such a way to make the “gaze” of Germany turn west and give Russian some respite.
So
Is Sea Lion a total waste of time and IPC? Well, I would agree with GHG that Germany going all out on Sea Lion is most likely a doomed strategy for Germany.
Thus if it is a doomed strategy you must go all out against Russia. That is Germany’s entire focus and just hold off UK/USA on the western front as long as possible.
Waste no time or IPC against the UK/USA besides bulking up the fortress Europa against them and everything else goes all in on Russia.
Now on G2 you still build the 8-9 TRS. Threaten Sea Lion and have the Allied players scampering around looking at You Tube videos on how to defeat it on Japans turn. You then take those TRS and move 18-20 units into Russia on G3. Make the Baltic sea a massive TRS shuck to Leningrad for INF and ART. That saves Germany 2 turns of movement to get INF/ART onto Moscow.
Bottom line for me is then Germany MUST fake Sea Lion on G2 with the TRS purchase to make the UK/USA react accordingly. Which means their focus is saving or liberating London ASAP and not doing crazy plans like middle earth or sending 12 FTRS to Moscow.
Fake Sea Lion, they have to respect it. Go all in on Moscow and crush them under your tanks.
By doing this you buy Germany/Italy 2-3 turns on the Europe map by making the UK/USA doing all the moves necessary to save London and not doing crazy plans on turn 1-2 like killing off Germany early and the Allies winning the game on Turn 10.