The basic uses of SQL are indeed easy to learn, but quickly you find out that many types of nested queries are no-nos.
You can see the impact e.g. in the R ecosystem where a good chunk of packages is bio related or the fact that the only user-friendly ontology tool (protege) and the main example of good use of related graph concepts is from bioinformatics
Unfortunately, I never used a graph database in a commercial setting, so I don't have much practical experience beyond just toy projects.
Since it seems like you are using this in a commercial setting, did you have any experience with Prolog as a query language?
Cypher is OK, but doesn't really follow any existing paradigms, and LPGs can be a massive footgun without a semantic layer since you can pretty much throw any property on a node type.
Federation over named graphs, or different sources as well.