It has aspects that are pretty exact, even scientific. Ever wondered why font sizes are in the increments they are, for example? Not to mention composition rules, color harmony rules, all the different grids, vertical rhythm etc. And there is the world of Prepress Production, cause it's one thing to make a 'picture' and entirely another thing to make sure it's being printed properly, esp when we're talking about hundreds of thousands of reprints. There are whole books that tackle the question of how to build blocks of text in a layout - between letter space (tracking), space between rows (leading), margins, number of words per line, viewing distance and so on and so forth. You're just accustomed to consume design daily, but you don't see it. That's the purpose of deisng, eps good design - you don't notice it. That's why you think you know everything about it. Does eating pizza make you a fucking chef?
Look at the fucking apps on your phone, your phone itself, the fucking chair you're sitting on. That's all been designed by some guy and now you're shitting on his head with your ignorance.