[wodenokoto]

I’m not sure I understand why it’s not only valid but more precise to square the length of the play.

If we assume that length of a play has an influence on the frequency of stop words, shouldn’t we compare samples of each play? (First x pages or y randomly sampled words)

[ncmncm]

It is an observed phenomenon. That doesn't make it a theory, it makes it a generator of hypotheses. It is another chore to figure out ways to test the hypotheses, and more chores testing them.

After one passes several different tests, it might be worth publishing, along with the list of rejected hypotheses. Then somebody else might identify a test that it fails, and another that could be tested, and might publish that.

Or, more likely, nothing comes of it, and you move on to other phenomena and other hypotheses for them. That's science. It always starts with, "that's odd, I wonder what it means." And, most usually, it seems to just mean "huh."