I don't really understand why you all hate Mark's shimmy.

I thought Candace's footwork needed some work. She didn't look relaxed,
You just made our point. Candace needs a lot of work in other areas. She can also probably shine, if Mark actually took the time to find what her strong points are. Derek & Cheryl do that with every single one of their partners.
Mark just likes to take the easy route. Put the girls in a lot of flashy fringe and make the shimmy for 8 seconds, so it looks like they do a lot of movement, when his choreography or work with his partners aren't very individualized, special or complicated. Dance move too complicated to take time to teach, no stick in an 8 beat shimmy instead.
I know a former, professional concert pianist I'll call Joe. Joe had a concert at Carnegie Hall once. He told me once that his brother was actually a better musician than he was. That playing piano came easily to his brother, who didn't practice his scales or technique the way he had to for several hours a day, to get to his brother's ease at playing.
But, in the end, it was his brother's undoing. Because playing came so easily, when it finally counted in the areas/levels he had to work hard at, he didn't. He couldn't appreciate the struggle. And he saw how much work it was for Joe to improve and he didn't want to put in that much effort. So he didn't make himself work hard to become exquisite at his craft, which may have made him at a world class level of musician. Eventually Joe surpassed him, having his Carnegie Hall concert and putting out a couple CDs.
I don't know, maybe Mark, being Corky & Shirley Ballas' child, maybe dancing genetically came very easily to Mark. And when he saw how much work Derek & Julianne had to put in, and keep putting in to improve and challenge themselves, Mark just didn't want to have to put in that much effort?
But, when it came time for the Olympics, Meryl & Charlie didn't call Mark, they called Derek. Yes, they wanted splashy show-stopping choreography, but they also wanted
better. That is not Mark. That is Derek.