You don't "need" Naval and Air units to play the game, however depending on the map you play and the country you are playing it might be best to have different types of units to support your mainland army.

A game can't be won by simply building planes and ships. Build units, and see what works for you.

of course, no matter what the doctrine or nation you played if you have a coast then you will likely can be invaded from sea. so, you need navy and seaplane, i didn't remember heavy tank can sunk battleship

yeah, i usually use small amount of them but in high level, but people i've meet using them in largescale.
and did not using rocket artilery or SPRA. idk why, instead of using buffed ornance branch they using nerfed air branch

Yeah I use air when playing comintern, their attack bombers are great, you may just have a interceptor problem but you can just give the default Soviet response and build more of them. Besides, there are many games where you don't even face an enemy air force at all...

As for navy, that heavily depends on where on the map you're playing, what you're doing, and what you encounter... but if you would need a navy with a different doctrine, you'll need one now as well.

update, i only go cruisers and destroyers, aircraft nothing.