Well, someone has to create the models. If You're lucky and there's plenty of good modellers in Your use case / hobby, good for You. Have fun printing.
What the OP however refers to is the "rapid prototyping" that 3D printers unlocked for masses. If You learn even some basic modelling (e.g. few primitives in OpenSCAD for programmers), it's trivial to do test fits and whatever gigs You need.
I haven't realized it myself until some months ago I needed a small funnel for a bottle. After some thinking I realized it's much easier/faster to throw together a difference of two cones and two cylinders in OpenSCAD in about 10min and print it in maybe another 20 than spend the time looking around stores to find some close compromise.
I think it's more like owning a computer without being able to use a text editor or a spreadsheet program. You can open files you get from other people but you can't make changes or generate anything original. Programming in this analogy would be modifying your printer itself.
Obviously there have been some successful computers where users don't modify their files, like mp3 players, but those are much cheaper and more user friendly than general purpose computers.
I suppose, I just don't use it that way. Have never printed something that I downloaded except for testing purposes. I use the printer to make stuff that I need around the house, like a bracket to hold my electric toothbrush charger to the towel bar, etc...
I check for well-designed looking ones first though, if it's not extremely custom (like the razor holder I designed to fit my specific razor over the side of my specific mug-like bathroom holder thing).
I found a nice looking bracket shaped specifically for my Bamix stick blender that someone else had designed, saved me some trial and error and time and filament.
I found someone else's design for a Makita LXT battery fitting that I used as the base to prototype the inverse: I wanted a dummy battery shape that I could mount to the wall in order to hang my vacuum cleaner from it.
I'm glad I can do some basic CAD / am willing to learn, but I've definitely got some use out of it with only a slicer. And then there are the people who only want trinkets anyway.
Those two projects made me realize that 3d printing can be a full time fun hobby for exploring all those things it would be too hard to machine in a garage.
I've been enjoying using OpenSCAD whenever I can (instead of Fusion 360). The language is a bit janky but it's great for hacking something up in a purely procedural manner, and using Git.
OpenSCAD is fine for what it does and I do use it a lot for very simple stuff. ImplicitCAD is another interesting project in that space that has fillet unions.
FreeCAD would be great if the Interface wouldn't be so janky. I give it a try every now and then, but never really get over the re-learning aspect.
So, I am still stuck with Fusion360 running in a VM on my otherwise FLOSS-only system :-/
