Well that is very true, Iam making some assumptions.
#1 if you have a CV you need two planes. Regardless of bought or on the board.
#2 If you have airbase it has 1-3 planes on it regardless of bought or on the board.
So, that is a total wash. The planes have to come from some where.
#3 A CV’s defense in a naval stack is of no importance. So, you have a stack of navy with a CV and 2 FTRS. You replace that out with 3 FTR land based units and remove the CV from the defense you are actually better off for inflicting CAS. Now, I will concede that a airbase on the coast cannot take a hit and absorb one CAS against you. That is the one advantage a CV has over a Airbase on the coast.
#4 Where again is this German CV moving again? It is not like a German CV is going on a rampage across the Atlantic headed for USA. It is sticking to the coasts of Europe or the coasts of the Med, where they also have Airbases to guard them.
Bottom line for me
There are very few places a German CV is needed because land based units on a Airbase perform the exact same function on the Europe map.
The Pacific map is a totally different beast and requires CV to move air power forward to project a threat. FTR and TAC on the Pacific map almost require a CV to move them into a position to attack.