In my experience SPARQL is really hard to use, and Wikidata data quality is really low. To the point that one of my larger project is trying to filter data to make it usable for my usecase.

Yes, I made some improvements ( https://www.wikidata.org/wiki/Special:Contributions/Mateusz_... ).

But overall I would not encourage using it, if I would know how much work it takes to get usable data I would not bother with it.

Queries as simple as "is this entry describing event, bridge or neither" are requiring extreme effort to get right in a reliable way, including maintaining private list of patches and exemptions.

And bots creating millions of known duplicated entries and expecting people to resolve this manually is quite discouraging. Creating Wikidata entries for Cebuano Wikipedia 'articles' was accepted, despite that Cebuano botpedia is nearly completely bot-generated.

And that is without unclear legal status. Yes, they can legally import databases covered by database rights - but they should either make clear that Wikidata is a legal quagmire in EU or forbid such imports. But Wikidata community did neither.