Did you have arrays in your jsonb data? I don't currently use jsonb for production performance sensitive queries, but in the past what I learned was that it's great at automatically indexing everything except arrays. You have to manually declare indexes on your arrays.

When jsonb works, it's incredible. I've had many... suboptimal experiences with mongo, and jsonb is just superior in my experience (although like I said, I haven't used it for performance critical stuff in production). For a long time, it kinda flew under the radar, and still remains an underappreciated feature of Postgres.