This sort of decline can't only be blamed on her coach though, whether it's Piotr or not. There is no reason why a 22 year old tennis player should be that much worse than she was at 18-20 years of age when she had the same coach. It goes beyond the fact that technically her strokes haven't improved in the last couple of years. If she was ranked at #5 or 6 and didn't constantly lose to non-contenders one could make the case that she's doing the best she can, but that those above her have just improved too much for her to keep up. But as it is she isn't even playing top 10 level tennis anymore. She's just able to (barely) hold on because she still enjoys a relatively high seeding at tournaments which allow her to avoid top players in early rounds. But if she had to start the season ranked outside the top 50 there's no way that she would work her way back up to the top 10-15 with her current level of play. Despite whatever technical (or tactical for that matter) problems there may be her biggest problem is without a shadow of a doubt mental. I'm not saying that she isn't trying, of course she is. But winning is no longer a matter of life or death to Caro. There's no fire there anymore, no spunk. She's become an excellent opportunity for lower ranked players to get the (on paper) "best win of their careers."
I fully agree on that. That's why in all honesty I think what's the best for her now would be to fall out of the top of the ranking. I don't know how, because she's very unlikely to finish her season out of top 15 considering the very weak field of players being featured there and even considering the months ahead on her worse surfaces, she's still on top 8 of the race to YEC.
But IMO she needs a true test of her will to be a top player...like last year, she played the only sparks of good tennis when she had to demonstrate she wasn't just a non-contendent anymore (Miami beating Serena and making Masha sweat for the win) and then when she had to catch the top 10 back (winning Seul and Moscow), but those were little challenges, she kind of felt to have achieved easily.
She would never do that, but I think a break from tennis or at least from the tour would do her really well...like skipping the whole clay season and figure out what does she really want to do and how. Keeping a top 10 spot shouldn't be a priority, hence it wouldn't be a disgrace if she was to skip the few months on the dirt...if her ultimate goal is to make money just by hanging in there, then it's all fine...she still can win a couple of matches in a row here and there.
In addition to that, I still believe that the racket is playing an important role in the whole story...I may be sounding like a broken record, but Agassi changed racket while being world n°1 and suddenly he couldn't win a match to save his life and he was on his way down, he didn't have a slam won by then and felt like everything was just going for the worse...he then switched to the old racket and immediatly started to win again and won his first slam...I am not saying that Caroline mathematically would do the same, but...