Well, from what I hear in the home theater industry, the content providers (Netflix, Hulu, Pluto, Tubi, Crackle) provide something like an API or framework, and the hardware manufacturers (Roku, smart TV manufacturers, TiVo) develop the apps. And in my experience, the Roku apps are usually better than those on smart TVs or other set top boxes. Part of it might be that they are dedicated streaming boxes, and so are faster than boxes that are also TVs or DVRs, and more robust than the "stick" formats, but the remote and the way features are used seems better to me. Plus, Roku has a big bonus, the ability to search for content across all channels. So the interface is proprietary, but it's based on the work of the content providers.
But as far as content, no, I don't think so. But I don't think that's what Roku is trying to sell, it's trying to sell a more convenient way to access the content you already pay for.