Is this Appeal to Extremes?

I don't think there's really any logic to dissect here.

The person, most charitably, expressed a subjective opinion about the quality of your writing. If they wanted to do that in good faith and open a discussion, they could have pointed to spelling and grammar errors or specific word choices, and compared to what reasonable expectations would be. But instead, they basically phrased it as an insult.

Any reasonable person reading your reply would realize that you're not being literal. You're stating an opposing opinion, that the quality of your writing is sufficient, and the reference to a classic author is simply a device to illustrate that their expectations may be too high .

Seems like a satirical retort to a semi-ad hominem attack

I'd say it's a witty retort. Well done!

Hi.  First poster here (!) - agree no fallacy, just opinion.

It appears to me as more of a snappy retort to a nasty message. I do, however, think that an argument could be made for the appeal to extremes fallacy. Put it this way, if I were the one who made the snappy retort I would argue against it being a fallacy, and if I were the target of the retort, I would argue for the fallacy.