Sentence Variation Affecting Essay Quality?

It's much too often that you hear "Sentence Variation!" from well-meaning teachers. It's often very helpful too, but has it any real use? Or is it just that sentence variation works well in good writing?

I decided to check it out, and let's just say that the results are ambiguous as of yet. I'm not exactly your Galileo type so I didn't do any exhaustive measurements, but just enough to exhaust my time. First off, locate some essays of high caliber (objectively) and low caliber (objectively).

My sources: NY Times for good, Bookrags (one of those essay-selling websites for naughty under-performing students).

So I whittled down the process to a few lines of code:

1) Copy and Paste the NY Times (good) essay into a cell and put quotes around it, remove all extraneous quotes inside the corpus.

2) Assign the essay to essayNYTimes

3) Now you must StringSplit it among {".", "!", "?"} and then Map that to another StringSplit among commas (to split the split sentences into words).

Now we're past the tedium.

4) Map the sentences you've gotten (the list with lists of words in each sentences, divided up among sentences) to Length

5) ListPlot it with the Joined function being True.

6) OPTIONAL Find the Mean of the words/sentences. Do the above for various corpora. Results:

I also did means, and the NY Times articles came out with about 15 words/sentence, whereas BookRags essays came out to well over 20 words/sentence. It's most likely due to the greater range of sentence lengths (I perused each essay and the poor essays seemed to have pompous sentences that hardly ever ended. Pithiness is golden.)