What catches my eye is the implication that in OSM features are "baked" into the map. More than anything OSM is a database. It is not so much a map drawing client. The client that you are referring to is probably the one on the view tab on the OSM page. That particular client's main purpose is merely to visually support contributors in making updates to the database.

In the database, nothing is baked in.

That said, the OSM foundation doesn't own the data. The contributor owns their contributions agreeing to license them under CC by-SA. Couple that with the fact that the specific OSM client you are referring to is open source, anyone is free to clone and extend it to their purposes (layers or what have you). If desired, their improvements to the client can be submitted to OSM for inclusion in the common if they are beneficial to map making. Or, an altogether new client can be created using the OSM database.

Nothing is baked-in in OSM. Contributors are free to add whatever (non-malicious content) they want, if there is no tag for a novel feature, then from what I've read OSM is open to additions.

OSM offers more freedom on all fronts.