I'm sure that what is built into One UI as of Beta 2 is basically the same thing as theme park, but you would think it would work with all the Google apps that have material you enabled (Chrome, Keep, Drive etc) but it's doesn't. Hopefully this will be fixed by the full release
I think the problem is the material you theme engine hasn't been open sourced yet. It's supposed to be in the Android 12.1 release in a few months, so Samsung is having to temporarily build one to meet consumer demands.
I don't think that's the case, afaik only the algorithm that picks the colors is proprietary but the themeing itself isn't. It seems like the colors work right one some of the widgets such as the Google clock widget