Either straits can be blockaded by a navy or they cant and are blockaded by armies and forts on the shore. The current "compromise" is where you can have 50 ships in a strait that is apparently realisticaly impossible to have ships in if you dont own the shoreline and those 50 ships cant block a army flying over them. Which one is it, either it should be impossible for ships to enter or for a army to cross.
The original poster is right. The screenshot he provided is narrow strait crossing bul**** to any logical person on the street seeing that picture. What is this historical example you talk about where a army crossed between the ships of a enemy fleet? And why was that example only possible if the empty province without any armies on the other side was owned by them?
The game is filled with abstractions. This is one of them. And ships not being able to blockade a strait isn’t the the same as not being able to move through it. The latter is a lot easier than the former.
As for navies being useless because of this... just no. Navies blocking straits was always a niche activity that only applies to a small number of countries and was always a silly exploit. It’s not what navies are for and it’s never been what they were for. If navies are ‘useless’ (which I don’t agree with) then the answer is not to allow them to block straits.