With any cichlid, aggression attitudes change with age.
Maturity can make a seemingly docile cichlid change almost over night, and kill tank mates.
Just because it has been docile for 6 months or a year, does not mean it will remain that way tomorrow.
Another factor is tank size.
A JD (or any medium size cichlid) may be less aggressive in a 6 ft tank, than in a 4 ft tank..
JDs are not piscivores like Parachromis, they are omnivores, yet even that can be influenced by tank size.
Any dither fish that can be easily cornered, due to lack of tank size, is at risk of being exploited as a protein source.
In nature, JDs are surrounded by live bearers like mollies, and gambusia, but in nature the number of gallons is in the thousands,
Expecting them to live peacefully together in a tank of only 50 gallons long term, is being a bit overly optimistic.
JDs and mollies living relatively comparably in nature in a video below.
Eden2