Even if that example was the only use-case (it's not, they are used for word similarity, sentiment analysis and more...), word embeddings would still be useful,

Even if that example was the only use-case (it's not, they are used for word similarity, sentiment analysis and more...), word embeddings would still be useful, since creating ontologies is not Easy and takes time. Somewhat unrelated, but the old joke goes: give one problem to two ontology experts, and they will come up with three different ontologies.