Agree
In nature FMs are a shoaling species (much like Geophagines, as they are the earth eaters of Central America), so keeping 1 or a pair is out of character for them, normally they would live a shoal of 4 -6.
I also agree that whenever a cichlid is line-bred, such as EBJDs, or even gold severums, by just focusing on trying to get fancy color, their natural robustness and immune response is also often sacrificed.
But even in nature when JDs share habitat with more aggressive species, they don't fair well.
Below are a coupe videos I took in Mexican Cenote's where JDs are endemic .
Eden2
In the video above, where JDs are the dominant cichlid, their population is high, and most are healthy.
But in the Cenote below where they are not the dominant cichlid, the JD population is low, and only the most robust survive.
027 zps4b102ffd
So trying to combine ill matched cichlids in the same small tank, is often not a success.
For some to live communally, a tank of minimum 300 gals may be needed.
Do the research and only combine those that coexist together in nature, in a proper size tank, and things could go well.
There are over 300 species of cichlids in Central and South America, many with differing thresholds of aggression, and requiring different water parameters.
Just tossing different species together because they are cichlids, and expecting them to thrive is not realistic.