The number of ringers and bad feeling about them.
To be fair, Amber and Lewis were only invited as replacements. Both had far less time to rehearse than the original contestants, who had 6 weeks. They would not have been able to get an absolute beginner to where they needed to be for the start.
Nikita was right when he said without Amber, he wouldn't be there and the show wouldn't be as good as it is, however unpopular that opinion is.
Contestants of their calibre and experience have always been on Strictly, and it's never been a level playing field.