The problem is, learning Perl allowed you to essentially get a fish for a day. Perl is not going to last. What you learned was essentially how to get a Rube Goldberg contraption to do what you wanted.
The symbolism in Huck Finn, however, is eternal. You can then read any great book, or look at any work of art, and understand it at a better level. What you've done is learned how to fish for yourself.
And so it seems to me that anyone capable of completing the assignment will have succeeded in little other than demonstrating how unnecessary it was for them to do it, and those that can't produce passing results will have gained no better understanding in the process of their failure.
The weight is in fact so biased to the side of redundancy that students routinely compose satisfactory essays without having read the book or understood it's symbolism or learned any skill but deception. And what does that say about the value of the assignment?
As a writing exercise the typical English essay may have marginal value, but significantly less than it would were the style subject matter not always so constrained to literary criticism, a genre which does not carry over well into others. The end product itself is practically worthless--the symbolism is as you said eternal and available to all at any time by reading the book. The only demand for English essays comes from people attempting to shirk creating their own.
I really don't think it's crazy for someone confident in their ability to succeed at such a task to regard it as less important than the challenge of developing a new skill and a tangible end product that is new to the world. I mightn't have have had the words to justify it at the time, but I certainly did feel that I was doing the right thing.
Perl not lasting is irrelevant. Perl was just the medium. Programming was the task, the art, that I got my practice in by wrangling that contraption. And it was practice I would not have gotten if I had relied on external rewards as motivation.
Putting extra effort into high school English can be totally worth it, but it is a personal preference that shouldn't be pushed on the unwilling.
Learning Perl isn't value-less, but it doesn't compare on any scale to trying "to acquire the understanding" of Huck Finn.
Would it be fair to ask you to prove your understanding and appreciation of Bob Marley by asking you to write an essay on him and then judge that essay based on whether it's contents matched up with what other people before you have said? It doesn't seem like that would help you understand if you didn't. It also takes away your own authority on whether your appreciation of the work is valid, which isn't educational at all.
I think your comment highlights the fact that it's normal to not "get" everything, too. That's something that seems to be disregarded in the curriculum, where everyone is supposed to get everything equally at the same time. If someone were to tell you their favorite albums were Kind of Blue, A Love Supreme, Legend, Pet Sounds, Thriller, Dark Side of The Moon, and Revolver, you wouldn't consider them a paragon of refinement so much as a liar. And yet, we're expecting something like that out of students by testing them this way.
I agree about acquired tastes; I've had a few myself. But people run away when something's pushed on them too harshly. Sometimes the cool assignments are the ones with a list of options (say, choose two from this list). It's an independent choice but still related to the material.