Modern Jive isn't Ballroom!
It ain't Swing, neither!
IMHO, some of the nicest looking MJ styles look almost balletic. I'm thinking of ladies like Katya & LilyB here, and they're fantastic. (I know! I know! they can both change & do other styles too!
, but for the purposes of this thread.... )
If you bend your knees too much it starts to look like old style R&R. Which is fine, if it's your style. But it's equally fine to have a different style, I'd say.
HTH!