It seems to me unfair that the invention of the corporation, the human creation of an immortal legal person, should destroy the way culture propagated all throughout human history before copyright was reified as "property" and people like you began advocating perpetual copyright held by such entities or passed down to heirs -- by remixing pre-existing cultural ideas, phrases, melodies, images. As Solomon noted in Ecclesiates, "there is nothing new under the sun." As more and more phrases, images, melodies are "owned" by such immortal legal persons zealous to collect rents on the "intellectual property", there less and less room for the creation of culture in the normal way, which always referenced pre-existing culture. Jazz would not and could not exist if your idea of ownership were applied by jazz musicians to their creations. You still haven't told me whether you really think that it should be harder to compose pieces like the Rhapsody on a Theme of Paganini or Fantasia on a Theme of Thomas Tallis because rightsholders have to be found and paid, or how that state of affairs would serve the Constitutional purpose of copyright.
Mickey Mouse should at some point become like the character of Robin Hood, the figure in Botticelli's "The Birth of Venus", or Beethoven's Fifth Symphony: something on which anyone can base derivative works, from which they can earn money if the market will pay them, without paying a "rightsholder" or being sued. So, yes it is both unfair and unconstitutional for Disney and his agents to use the law to "maintain profits from the creative efforts of Mr. Disney for an indefinite period of time" if that maintenance requires the enforcement of a monopoly on the creation of derivative works.
Disney has benefitted mightily from remixing pre-existing culture: Snow White, Cinderella, The Little Mermaid (Did they pay Hans Christian Andersen's heirs for the rights? No. The story was in the public domain, the normal state for stories, not locked up in some corporation's horde of "intellectual property"), Beauty and the Beast (They were really happy that no corporation was holding the rights to the works of Jeanne-Marie Leprince de Beaumont on that one), but try to remix Mickey Mouse and their attitude toward cultural appropriation from the past reverses.
You might ask yourself why the Founders didn't give Congress the power to grant perpetual copyrights, but specified "for a limited term". Get back to me when you've figured out the answer. Hint: it has something to do with Science and the useful Arts having a value beyond the merely commercial.
There is a fine line between incentivizing creators and discouraging them. Copyright law attempts to tread that line. There is no reason any person cannot create ad nausea duplications of works that have gone before. In fact, I’m sure it often happens that humans have the same creative ideas at the same time - even ideas that are incredibly complex.
Copyright law merely assigns who will receive substance in return, and for how long. The upside is that you have opportunity to create and bring to market indefinitely something no one else may receive substance from. The downside is the fees and a robust effort at swatting down any duplications another party may try to benefit from. The market place tends to crystalize where the money goes in consuming what is created.
If Walt Disney had expired without expressing any wishes as to how his creation should be handled in the marketplace, someone else would likely have taken up the torch to make money off of Mickey. I harbor absolutely no animosity toward those who would like to preserve an income from that creation, and no desire to market a Mickey Mouse of my own. But I may one day develop and bring to market an animated figure that is more interesting, profit from it, and enjoin the law to sustain that benefit as long as possible.
You’re absolutely right in quoting Ecclesiastes in regard to these matters. All is vanity.. Walt’s creations, along with everything done under the sun, will one day fade into nothing, along with all the perceived profits. Meanwhile, I see no reason to begrudge excellent creators and their creations benefits due in this short epoch we call history.