Some dude coined these terms, and they caught on for a while during the cold war. Third world typically being of little interest to first and second, and often poor.

So eventually "third world" came to just mean "poor countries". After all, there has now been as much time, post WWII, without the cold war, as there was with one!

Which would make Ireland, Sweden, Switzerland, Australia, Japan etc third world.

That’s not how the term is used.