I’ll admit, there isn’t a lot of science to this post. Bonsai itself isn’t much of a topic for research and it gets used as a name for a type of decision tree which confuses searches.
To answer this question I will borrow Colin Tudge’s definition of a tree: “‘Tree’ is not a distinct category, like ‘dog’ or ‘horse’. It is just a way of being a plant.”
Similarly, “Bonsai is not a distinct category, like ‘lichen’ or ‘flowers’. It is just a way of being a tree.” The bonsai way of being a tree involves living in a very small pot – in a space that’s much much smaller than nature ever intended – and, that’s pretty much it. Everything else is aesthetics!