A rendering engine is not a browser. Are all the Chrome engine variants really just Chrome in a skin? I don’t think so they all have unique properties that set them apart. As do Orion, Firefox, brave, etc on iOS
I wouldn't consider other chromium browsers reskinned because they're using the chromium engine as a dependency, by choice. They can customize it as much or as little as they want (and I'd imagine they do to various extents).
Browsers on iOS can't - they are required (legally, not technologically) to use (a worse version of) Safari's engine. Chrome for iOS is not the browser that the chrome team wants to distribute, it's a browser Apple made that has been customized to the extent that Apple allows it to be customized. What is that if not reskinned?
It's worse than that, even - IIRC the renderer that other browsers have to use is slower and more limited than the one Safari uses.
So other browsers are effectively reskinned hobbled Safari.