Caro had trouble with her knees last year (or at least she says so). I don't see the big difference, Ksenia has been ranked in top 40 too last year and has fallen down the rankings due to injuries ( or at least other people here say so). Look at the hard facts, Petra is ranked 8th, Caro 10th, both have work to do , there's no way around it however much you like to twist it.
It appears you totally missed the point of what UncleSilas was saying.
You're focusing on ranking. And for the record (since you brought it up), Petra was in the top 4-5 for most of the year, until after the US Open, when ailments got to her and she really took her slid.
More importantly, UncleSilas was focusing on ability to win a big match due to weapons and talent. And in that respect Caro and Petra are not even in the same ball park or discussion.
One match here or there, and some one can make the argument Petra could have won the Australian, Wimbledon or The French Open last year (she made the semi's of two and the quarters of one), Caro was never in that position in any of those tournaments. And (unlike Petra) very few people would give her a chance of winning, if she even got there. Why? Because she has no weapons and always has to be sharp (or in Marathon mode) to win. Big difference!
So the ranking means nothing, as it's never meant with Caro, in ones ability to compete for or win majors (though Of course in Petra's case, it can be a barometer of her overall sharpness, consistency and health for the year). Apples and Oranges.
Nothing else needs to be said on this.