I imagine that saying “every property is up for grabs” would give a massive advantage to mega corporations with the resources to start mass-marketing half a dozen shows at once.

No doubt about it, there should be SOME copyright. But big corporations are going to be avantaged no matter what in this particular category. Without copyright, big corps can snag up anybody's content without compensation, many content makers may not even bother if this were the case. With copyright, big corps always have the money to persaude content makers. If the content maker doesn't sell out to big corps, their family/estate likely will sell out to big corps.

A properly limited copyright is the best option. When the United States was founded, copyright was a maximum of 28 years. Sure, big corps can eventually mass produce the original content maker's content as you say, but the content maker will have time for their work to stand out on its' own while getting compensated, then EVERYONE, not just big corps, will have a chance to make their own version if they so desire, therefore actually giving competition to the big corps.