With Prusa being so open sourced, I'm willing to bet they will open an API on Printables once they get things smoothed out a bit. They are still polishing up the site and molding it into what the community is looking for. They started out rough, but quickly took feedback and changed the site.

Even now, I find myself checking Thingiverse for a "thing" now and then when Printables fails to have it (yet).

Cults is an interesting one. I like that Thingiverse and Printables remains free, so I like that Cults has found itself a niche to have paid models. Cults would be a hard one to compare against for this fact alone.

Thangs is similar because they "pseudo paywall" everything behind requiring a login, which immediately puts some people off. (Yes, having a login for the other sites unlocks many "features", but some people want to quickly grab a file and go. Or want to download a file with some form of "privacy ")

I am unsure about Creality Cloud as I haven't used it.

In the end. Yes. I fully agree many people got their start with Thingiverse. MakerBot used to be a great open-source company, Zach Smith really helped get Thingiverse running and opened the door to helping the community. After Bre Pettis pushed Zach out and went closed source, the community rallied to get Thingiverse to remain open. After the Stratysas takeover, it was obvious they quit putting any money or effort into the site. Thankfully the open-source community stepped up and started working on alternatives.