If I had to guess, it was the Illuminati (since they clearly own all the SaaS vendors) that brought us the Semantic Layer, but we will find won’t we?

It's interesting how this is both a nebulous yet concrete idea and how definitions and implementations vary widely. I was having the _exact_ same questions since I've had to newly lean more into the data engineering space at my current gig, so it's helpful to hear these takeaways from folks experienced in the trenches (not just the newbs).

a semantic layer produces eggcorns

Looker?

I believe the author missed another approach of the semantic layer. That is the one used by Power BI Semantic model or, and perhaps, the most interesting one Malloy. In these tools, the semantic layer is a thin layer that only define the following: - metric definition (mostly as aggregation function) - dimensions of analysis (product category, country, etc.)

This blog makes a much better argument than I would at presenting why Malloy is a really interesting and welcome innovation in Data Analytics space : https://carlineng.com/?postid=malloy-intro#blog