Joy, you beat me to it. Thankyou.
My daughter found salsa very easy, but could not dance "blues" if her life depended on it. Of course, my daughter has had structured/formal dance training since she was a wee one.
If she could learn to dance such "unstructured" dance forms, it would step up her dancing immeasurably. (maybe one day when she is older.)
You have to remember that in blues dancing while some leaders can be
individually musical they can't bring that musicality into the
connection they have with their partner.
I firmly think that in any partner dancing like blues, swing, bachata, salsa or tango, etc the connection with the partner is
first and foremost, connection with the music the
next, and then follows all the rest - the dance floor, technique, sequences, yada yada. So if you have a couple who have everything pat down but not a good connection between them on the dancefloor it is going to suck for either one or the both!
Discussing with other dancers (albeit a small sample of half a dozen or so) who are proficient in two or more, social partner dance forms (minus ballroom), the consensus seems that if one were to plot each in terms of degree of difficulty from least to most hard to learn/dance it will be something like:
merengue<blues<bachata<salsa<swing<tango
Of course personally some may find adjacent ones to flip (e.g. bachata<blues).
Now think of adding something like Kizomba and Zouk into that pic.
Another key difference between dances like Bachata, Blues, Tango (& Kizomba) and the rest (salsa, swing, etc) is the comfort with intervention of the personal space due to closeness or close hold/embrace that is largely preferred.