I dunno. I think there is a difference. The showrunners make choices about fictional story ideas. They (nor anyone) has control over new facts about science. I think that makes it a bit different. Perhaps not to you, but overall.
But your question was specifically
about me and people like me. Wthin the parameters of the question as you yourself defined it, a question about how we, the writers feel about it, my answer is that for me, there's no functional difference. In neither case do I have any control over what new information may be revealed after what I wrote has already been published.
If there is a difference, it's that in original fiction, a writer sometimes has the opportunity to re-release it in rewritten form to correct scientific errors, as I did when I expanded "Aggravated Vehicular Genocide" into
Arachne's Crime, or as Poul Anderson did with some of his early Dominic Flandry and Nicholas van Rijn stories when he later collected them. But there's at least one case of that happening in Trek, with Diane Duane's novels being adjusted in
The Bloodwing Voyages to make them slightly more consistent with the canon timeline.
Yes, when it comes to story ideas it may be a blind choice in the sense they may not even be aware that some novel may have already covered that story idea (and it very well may not make a difference if they did). But they can choose to do that, or not to do that when it comes to a fictional idea.
Because it belongs to them, so they have every right to do whatever they want with it. We're just hired contractors working on their behalf. It's like getting hired to paint someone else's house. It's not your house, so you don't get to feel proprietary about the work you did there. They paid you to do it, so it belongs to them, and it's theirs to do with as they please, without you having a say in it. It would be foolish and unprofessional to get upset about that. It's just not the same as the work you do on your own property.
It's
because I value my control over my original universes that I defer to other people's control over their universes. I think about how I'd feel about letting someone else write in one of my worlds, how I'd want them to respect my vision of the universe and my control over how it goes, and I try to behave the same way when I'm the one invited into someone else's universe. I respect their ownership of their own property. I don't get upset that I don't get to be in control, because I have no right to expect to be.