as if land/air part of the game is super realistic
Yes, you can also make unnaturally large armies and air forces. I'm opposed to that too, especially when I invade minor nations and have to deal with way bigger armies than they had in reality. It's also bad for game performance. I'm glad there are mods like Expert AI that allows you to modify how much minor nations can do.
Given how long it takes to build ships, I'm not sure how making them easier to obtain would be done. Increasing the number of dockyards you can build, or shortening build time, both feel incredibly gamey. Either way, I like that ships are a huge investment and that sinking enemy ships actually feels very impactful.
Now, if there was some way to implement smaller ships like frigates, corvettes, and commerce raiders made by putting guns on merchant ships, that'd be a more feasible way for minor nations to build navies. They wouldn't even have to be implemented as actual ships, maybe more the same way as air wings - assign them to a port, and they project a zone of control that interdicts convoys and maybe even has a chance of damaging or sinking the odd enemy ship, particularly in Fjords & Archipelagos terrain.
But building a sizeable navy as Norway or some other minor? Nope. The smallest ship represented in HoI4 is the destroyer, and even that is a really big ship. It shouldn't be easy for minor nations to build those.
but when it comes to navy everyone suddenly want it to be realistic !
To the contrary, lots of people dislike the division spam part of the game, both for the unrealistic nature and for the performance hit.
Yeah, but this is a game it shouldn't take 2-4 years to build 1 battleship. Everything except submarines is just a waste of time and resources.
A game based closely on real-world industry and history. I absolutely think a capital ship should take several years to build, as they did in reality. But yes, building battleships was a bit of a waste of resources in WWII. Investing dockyards in them is something you should have to consider carefully.