Computers don't rely on electricity?
Crisper doesn't rely on DNA?
Combustion engines didn't rely on steam engines?
Vaccines and medicines didn't rely on previous medicines etc.
It's previous ideas all the way down.
It baffles me how firmly people tend to think in "either / or" propositions.
I don't know of anyone that argues that originality and creativity do not build on top of previous ideas. To state otherwise is to straw-man so spectacularly that the conversation has gone completely off of the rails.
The premise being discussed is simply this: Is there such a thing as "original thought" ?
The reason this question goes off the rails so quickly is because it is philosophical. It is very hard to bring that into pure objective measurement. And so it tends to bring out the people think that free will exists vs the people that think that free will is an illusion. And yes, it boils down to free will because in order to have "true" original thought, you need the element of free will. The "free will is an illusion" hypothesis boils down to the idea that your brain is a type of machine controlled by various inputs / external stimuli and that you have no control over thoughts that enter your mind. There are some interesting studies that get cited that support this hypothesis. The counter argument from the "free will exists" point of view is that while you might not able to control random thoughts that enter your mind, you can still choose which thoughts to focus on and to act upon.
Therefore, the logical refutation to your straw-man is that while iterative creations build upon previous ideas by definition, they still require some element of "newness" to be a "creation." This newness may be combining and mixing various previous elements together (which is often an argument made by the "there is no such thing as genuine original thought" hypothesis since their claim is that ALL creation is the combination of previous ideas), but that "newness" could also, hypothetically, include an element of something entirely unthought of previously.
You don't need to disprove that creation is iterative in order to prove that it is possible for someone to have a genuinely original idea. But to muddy the water further into philosophical musing, could it not be argued that thinking to combine elements of previous ideas that no one had ever thought to combine before IS a genuinely "original" idea? If our brains are just machines that take inputs, combine them and return outputs, then why isn't EVERYONE creating "new" inventions all the time? Why do we recognize that "some" people have a creative gift while others do not? Why is "exceptionalism" widely recognized in creative endeavours if it doesn't exist?