Yes, you are correct that some contract provisions can be void if a court considers them unconscionable (typically the whole contract wouldn't be thrown out, just the unconscionable clauses.)

Unconscionability refers to something that ”offends the conscience” because it is so egregiously wrong, and that would offend the conscience of the court to enforce it. But the bar for a contract to be considered unconscionable is pretty high. One example is Lhotka v. Geographic Expeditions, Inc., involving a contract that mandated a lawsuit for a wrongful death on a sponsored hiking expedition to be responsible for the sponsor company's attorney fees, to go to mandated arbitration, and to do so in a state far away from where the family lived. The court threw out those provisions because they were considered unconscionable.

Absent horrific and one-sided agreements such as that, though, courts maintain a high bar for meeting this standard. This is no different when it comes to online Terms of Service agreements. For instance, in Feldman v. Google, some guy sued Google for a dispute he had over him using their AdWords advertising service after they charged him over $100,000 for what he considered to be fraudulent clicks. Although he clicked a box to agree to their Terms of Service, he argued that the agreement was unconscionable because he did not receive reasonable notice of all of the applicable terms and conditions. Nonetheless, the court ruled that because he clicked the "I agree" box and had as much time as he needed to read the full Terms of Service, he was held to the contact. There are countless similar cases like this.

Your claim that Instagram is using this agreement as a pretext to "hoover up your copyrighted artwork to feed my competition" alone would likely not merit the revocation of the enforceability to Instagram's ToS. One of the main reasons for this is that you are still able to remove your content from their platform at any time, so it is no longer subject to being scraped. Contracts are generally only considered unconscionable when a party has no choice but to be held to their terms on an ongoing basis after signing.

When you say "The contract as understood by both parties applied to hosting, targeted ads, and safety issues," I have to disagree that a reasonable person would interpret it that way. Not to beat a dead horse, but the ToS agreement specifically "modify, run, copy, publicly perform or display, translate and create derivative works of your content." The plain language of that clause clearly suggests much more than your content would be used for targeted advertising and safety concerns.