Interesting thought, Tom. I’m not sure what I think about that. For one (working in SEO and content marketing) Google hates anything under 500 words. Beyond that, it’s hard to get anything to perform around that word count because there’s often a lack of depth. And then there’s the thought that, if you’re publishing on Medium at 300 word lengths, then your average reader time won’t be all that significant – which is what brings in the money, if that’s what you’re trying to achieve.
I guess it all depends on your objectives.