So, it's common for an Author to focus more so on the main characters than anyone else.
Never denied this, read my post again, I said sometimes
The side characters get their fair share of plot development, just not as much as the main characters.
Shino,lee,kiba,hidan,Hamura,neji,temari and kankuro
"Fair" yeah sure
Shino is an uninteresting character in general. There wouldn't be much to say about him.
That's just your opinion though, to me he's more interesting than both sasuke and narutp