This is probably the best explanation that I can imagine -- that they're not fundamentally different, just that ECS tends to make a sufficiently different set of design choices that it warrants some of it's own terminology.

I can't help but wonder what a more generalized take on ECS might look like, if it were to continue drawing from relational databases. For example, support for multiple indices to assist with different query patterns. Or triggers to abstract away cascading updates. Or perhaps materialized views to keep query patterns simple.

I've never had the opportunity to use an ECS system, especially in a performance sensitive context, so I don't have a good sense of where any pain points are in practice versus what my imagination can conjure up.

I also wonder what it might look like to use SQL to generate an optimal C++ representation while keeping the data definition high level.

Just idle musings - maybe one day I'll take the time to experiment.