I don't think Eddie really deserved a 10 from Shirley, although his dance had energy and suited his personality. That's the thing about street dance, the dancer can improvise because, as far as I can tell, there are no proper rules. In my training days, 1970s, we learnt old-school street dances like tap dancing and break dancing, but new-school street dance has moved on to hip hop, house, and techno.
I don't think Eddie and Karen necessarily needed to be in perfect sync as long as their movements as a whole were sharp and rhthmically snappy. From what I recall, Eddie's quick, short steps didn't change into long, smooth steps as fluidly as Karen's did. She bounces up, down and across with ease.
I would have given Eddie 8, but others who mainly focus on the spectacle, might have said 10 like Shirley.