Slower play .. and already at the beginning another planning ..

.. aim to compose stacks of each 5 or more of SP-AA and at least 3 or more other types of armored units - lethal to any attacking air force ..
.. stacks of AA and other unarmored units secure the provinces (in bunkers) and follow the front, as soon as "the air is clean" ..

(..there are more different ground units with also better SBDE than types of planes available; compare the ratio of combat values; from day 16, air force will become increasingly superior to unarmored AA / unit stacks, but gets worse against (good mixed) armored unit stacks with SP-AA; ..of course, a little own air force is also not wrong..
..but e.g. an ally and me have in this way smashed a coalition of 4 members that had more than 3x so many planes as we.. - ..rockets are still a danger, but "a lot of move" helps.. )

1) In most cases, local air superiority is an advantages. It forces the enemy to protect with AA/SP AA in their stacks. You can recon from a distance to see what your opponent has in his stacks. The longer the range of the superior air force, the larger the advantage.
2) It is useful to be able to field a large air force. You only need to build an air force sufficient to have local air superiority most of the time.
3) What you need for an air force depends on what the size and quality and skill of the enemy is.
4) Sometimes you can take out the enemy's airbases. Sometimes you need some AA/SP AA to take out an air base.
5) AA/SP AA can help against an airforce.
6) To counter most air forces, you will need some sort of air force.
7) Some players are heavy on tac bombers with few interceptors if any in the stacks. Interceptor/tac stacks on patrol against them can cut the stacks down a lot.
An advantage in interceptor level can be a significant advantage/disadvantage in a dog fight.
9) Sometimes you can blitz the airports.

I generally use a lot of artillery and not a lot of airforce, except in cases when the enemy has a lot of airforce that I need to counter, or I will have to defend allies over a large area.

It is not that difficult as some think, to operate more with ground forces and at the same time prevail against players with air force priority.

And apart from the option to stay online during air battles and manually control own planes (to restart the patrols), against big enemy air forces it's even far more efficient to deploy well stacked ground forces (SP-AA and other armored units - as described above - and more useful thereby are several different armored types than too many of the same type) as wasting the own planes in wear-out-air-battles ..
(which is just as wise as e.g. to line up with 25 tanks + 25 ATs vs. 25 ATs + 25 tanks, or with 40 infantry vs. 40 militia..etc..)


Of course, one have to be courageous enough, to research and to build the appropriate units instead of more planes, but the point comes where enemy planes bite off their teeth - when the paper becomes as hard as stone the scissors cannot cut it any more ..
.. then the advantage lies with the one who can already muster more (and better) ground forces ..

If someone can not withstand against planes before day 16, he probably has not already understood the game correctly; if someone can not resist against planes after that, then he probably still does not understand the system of connecting and assembling combat units with regard to the respective combat values of the different units.

If you are playing in one of the historical rounds, rockets are a major trump card. The trick is to produce maximum level 1 rockets first (as they require smaller airbases) and then upgrade to rocket level 2 which cannot be shot down. I generally first attack all my opponent's important cities with rockets to cripple their industry, and then invade from land. I don't maintain a huge airforce as such but I do keep a number of tactical bombers which are very useful against tanks as well as anti tank units.