I’m not sure we are talking about the same thing here. Sure, if you are creating a basic blog or marketing site, then you can survive with a handful of content types along the lines of Wordpress authoring as the data capture requirements are fairly simplistic and it’s mainly text content that you are capturing in the model.
But, if you want to create a more sophisticated application with complex data capture, multiple hierarchies & many relationships then you need a lot more content types just to store that data. For example, we can’t take a relational database with 200 tables and flatten that into 4 content types. The model is just way more complex than that.
We also need to be able to offer editorial staff more sophisticated ways to format articles beyond the basic formatting options in the standard rich text field, e.g. responsive grids, tables, review cards, callout boxes, floated images, etc. These need to be embeddable at any place within the rich text field.
So, we create additional content types to capture just the data for these embedded pieces of content and then use custom content renderers to render the rich text content as HTML in the web application with the appropriate layout & styling.
Are you able to share a link to the site you are referring to that is authored with just 4 content types?