When I said RDBMS, I meant those that have a client/server model. The versatiles docs talk about the complexity and surface area of database systems as a motivator for creating their own container format. From this I inferred they were referring to Postgres and PostGIS, which are used in the canonical OpenMapTiles implementation.
Watching that video, they do mention not liking the traditional Postgres/PostGIS approach due to its heavy weight. But they also say they disliked mbtiles due to its SQLite dependency, and that the versatiles format is inspired on/based on pmtiles. (Apologies if I'm missing nuance here, I was watching auto translated auto generated captions.)
I found https://github.com/versatiles-org/versatiles-rs/issues/24 which contrasts the versatiles format vs the pmtiles format. After reading it, I'm not personally convinced of the benefits of versatiles vs just throwing a CDN in front of a clustered pmtiles file, but perhaps I'm missing something.