To my knowledge, nobody has ever claimed that there should be “one ontology to rule them all.” Instead, what is regularly promoted is ontology reuse and/or integration. For example, the FOAF ontology is widely used in the semantic web to describe persons; why create your own ontology when you can reuse a well-established one? Integration of ontologies allows for conciliation of perspectives, causing data that use these ontologies to become meaningfully related. Admittedly, there are some rather large, comprehensive ontologies out there, and there are some very popular and pervasive ones, too. However, there is no standard or recommendation that requires publishers of RDF data to comply with any particular ontology. You could even ignore the RDF vocabulary if you so please (yes, even rdf:type).

The primary purpose of an ontology (in my view) is to attach explicit semantics to your data. Just as the participant had stated (although he meant it in contrast to the semantic web), there are many ontologies. They compete in the ecosystem of the World Wide Web and evolve accordingly (or become extinct).

RDF is meant to solve the problem of meaningfully publishing data (not just documents) on the World Wide Web. Beyond that, do what you want. More specifically, when you crawl and/or aggregate data from the World Wide Web, you don’t have to keep the RDF data as triples in your system. It is no longer on the global stage of the World Wide Web; rather, it is now in your system where you are king. So optimize away! Store it or process it however you like! Relational databases? Sure! Rewrite URIs as shorter terms? Whatever floats your boat! Ignore the explicit semantics and treat it like an unlabeled graph? I wouldn’t recommend it, but you’re the king! Do whatever it takes to meet your use case, and if your use case has something to do with RDF data, then fine, leave it as triples if you want. My point is, it’s not necessarily “RDF all the way down,” but it is “RDF at the top” where “top” is the place of publication, the World Wide Web. The universal naming mechanism of URIs and the generic data model enables data publishers to get data out there in a way that can be explicitly understood by machines (for example, when I say “Beast is furry,” am I talking about Mark Zuckerberg’s dog or the fictional X-Man Dr. Henry Philip “Hank” McCoy?), but as the creator of that machine, it’s up to you how to utilize those explicit semantics.