Szczecin has been 3rd tier city since many years
The one time I was there (many years ago) I was surprised to see what a dump it was. One of the most poorly maintained cities I'd ever seen in Poland. Is it any better. One friend's explanation was that they didn't want to make it look too attractive to the Germans across the border....
Horizontally speaking, It's central Poland that is better developed, peripheral areas on both sides (+ a lot in the north) are falling behind
I pretty much agree with this. Draw a line from Warsaw to Gdańsk, Poznań, Wrocław, Cracow and back to Warsaw. Most of what's inside that area is pretty okay and most of what's not inside it ...... is a lot worse off.