Unfortunately the music field never had such collaborative effort to build a unified ontology, so each big player have its own ontology, and they are not very compatible. From personal experience, building software that consumes data from multiple sources in music is a nightmare, it is impossible to design a data model that fits all the incompatible ontologies.

Agreed… and it’s too late to fix it now.

Relevant XKCD: https://xkcd.com/927/

The scope of those is pretty limited (i.e., helping people categorize their discogs with a dozen or so common fields) and isn't really a "musical ontology" where you're hooking it up to a first order logic solver and reasoning about music or whatever mythical use case drives most of that work.

Sort of... They are used at scale to share and ingest data between services, for things like recommendations, etc. But it is messy, a lot of the ontology is more or less the same but every company/database does things slightly differently.

Most of the difficulties are with matching artists and content across different databases, which is a separate issue. The ontology itself is tangential, but one example where it's important (even if it's not a fully / cleanly solved problem).