Is it just me or are the majority of plugins for WordPress simply wrappers for interacting with the DB? (In the sense that there's no need for them in more modern CMSs that feature structured content functionality out of the box)

Actually, it is best practice to use the WordPress functions to modify content in the DB.

Direct interaction with the DB should only be considered in the rare cases where WordPress' content structure can't be adapted to suit the plugins' requirements...

Unfortunately, many devs ignore the possibilities WordPress provides and just mess with the database directly.