There are two distinct points here. I am discussing an Issur Gezel, which obviously requires the victim to have had ownership. Hence, I am citing the numerous Poskim who rule that there is ownership of ideas. Once we accept that the accepted Halacha and vast majority of Poskim accept intellectual property, it is little different than the theft of any other possession. However, there are some slight differences, as I mentioned previously regarding inheritance. I cannot steal you object even if I would not have spent money to purchase it otherwise.
However, this argument is absolutely irrelevant to the prohibition of Gezel, and if there is Halachic ownership of intangible ideas, this Heter is totally spurious.
I hope this answers your well thought-out question.