Can't speak about Prisma (or Postgres much).

But I've found with that you can get better performance in _few_ situations with application level joins than SQL joins when the SQL join is causing a table lock and therefore rather than slower parallel application joins you have sequential MySQL joins. (The lock also prevents other parallel DB queries which is generally the bigger deal than if this endpoint is faster or not).

Although I do reach for the SQL join first but if something is slow then metrics and optimization is necessary.