Some people take the stance that even using view counts as part of ranking should result in a company listing section 230 protections, e.g. https://news.ycombinator.com/item?id=46027529
You proposed an interesting framing around reproducibility of content ranking, as in two users who have the exact same watch history, liked posts, group memberships, etc. should have the same content served to them. But in subsequent responses it sounds like reproducibility isn't enough, certain actions shouldn't be used for recommendation even if it is entirely reproducible. My reading is that in your model, there are "small" actions that user take that shouldn't be used for recommendations, and presumably there are also "big" actions that are okay to use for recommendation. If that's the case, then what user actions would you permit to be used for recommendations and which ones would not be permitted to use? What are the delineation between "small" and "big" actions?
Labeling is another idea but Meta does, in fact, disclaim which user actions are used for content recommendations: https://transparency.meta.com/features/ranking-and-content/
Basically, I still don't have a clear picture of what does and doesn't qualify as "algorithmically served" content in your model.