No they will just wait for the timer to tick away and monopolize on a community that someone else spent years building. Just because you change the law in your thought experiment for it to be legal doesn’t make it not exploitative. If we legalize slavery you can’t just say, “well its no longer exploitative, its the law”
And yes, if it is good, people will jump on it. Evidence being that HBO did not wait 170 years to start making game of thrones. They saw a story they could sell, so they paid the author to make it. If they did not, another media maker could and would have. Warner brothers did not wait until Harry Potter copyrights expire. I am sure other media makers were bidding for Harry Potter rights too.
Of course, Martin and Rowling have been paid less if copyright was 10 years. But would they have written the stories if they earned $10M instead of $100M or $1B or whatever they earned? I would err on the side of yes.