Thanks for the hours put into testing! I will do some tests myself with it and see if I can get Rive to work. If I can get it working I will submit it here so you can try it out.
As for why I picked Rive, it was for a variety of reasons mostly coming down to these points:
1: I wanted to be able to use vector graphics, since they scale cleanly and usually take up less space if done correctly. Raster graphics work, and is the primary graphics medium used in most VN's and engines. I think because it requires less processing to morph raster graphics than vectors, not sure though.
2: I wanted to not only have skeletal animation, but mesh deformation. With the deformations I could do character turns. DragonBones does have mesh deformations but it uses only raster graphics not vector.
3: I wanted it to work on my Linux OS. Most tools like DragonBones are Windows/Mac only. I could use a Windows system if need be, but would prefer cross platform tools. If DragonBones was the only method that worked best then I would install windows for it.
4: I wanted it to be free to use. I had originally looked at Lottie/BodyMovin https://lottiefiles.com/ but it mainly uses an AfterEffects plugin, but AE is a paid software. There is also a Figma plugin but its using that service which could cost money. Rive is free but sadly is only a web based editor. Dragonbones is free and offline which makes editing easier.
I would love to find a tool that does what Live2D does https://www.live2d.com/en/about/ but its a paid software as well and only windows if I remember correctly. The closest free alternative I have found is Rive, and with some of the things in their roadmap they will eventually get to a nice alternative, but not fully there yet. Dragonbones would be the next best to fit this criteria.
I thought DragonBones had to use a runtime as well though: https://github.com/DragonBones/DragonBonesJS now if it can do it without runtimes that is very cool too. I will have to research it again, but still limited with raster and windows though for the editor.