I agree that Kerber is a bad match-up, but I disagree that she has a good serve. Her second serve is one of the most pathetic deliveries that have ever existed in the top 10, and I say that bearing in mind that Errani is in the top 10. If Ana were to beat her, it'll have to start with attacking Kerber's second serve.
But you have to take into consideration the fact that Kerber is a lefty. She will serve to Ana's BH with angle.. it could be the most pathetic, slow serve ever.. if its angled to the BH Ana either makes an awful return or doesn't return at all.
I've been meaning to address this point for a while...I don't think Nigel aims for her to go that average route. Remember at IW during the QF his on-court advice for her was to 'wear the pants' and to 'make her feel the forehand', which she promptly did. Given that the Montreal court is slower than the average USO court, more similar to IW courts (IIRC), she may have a chance to do that.
Nigel is working with Ana on adding spin, adding air to her shots, and having a less risky game. Within that, he wants her to be aggressive, to control points.. but if you are working on putting air to your shots, you are already going to be less aggressive.. and being a tiny bit less aggressive in Ana's case already foresakes control to the other player.. because Ana is not fast enough or tennis smart enough... and you do what you are working on. When she faces top players, they are more aggressive and better at the average game.. happens what it happens, she has been crushed by the first top player she gets in basically every single tournament this year.
They are both taking an average game route, its something they must have agreed on. And this route will always lead Ana to being an ordinary player. It's the opposite route from the aggressive mentality really.. because it pleads for a less risky game. Nigel wants Ana to be aggressive within that average route.. but I think that is extremely hard for her to do. Ana needs to flatten out her FH to make it a real weapon, to be able to be really aggressive with it, to get it heavy and hard again.. yet she is working on making it less risky and adding air to it.. its like having to do something in a match that is the opposite of what you are working on during practice... Its just a 180 spin on mentality for the game.. on how you approach the game play.
The one player who mastered the average game route is Vika, IMHO. She is aggressive within that average route, aggressive without the risky game. But she is a fast player, who has some tennis smarts and who can keep the ball deep 90% of the time. Ana can't play like that at all.. and should never ever even attempt it.. yet sometimes I feel like she is trying to do that... run a lot and hit without taking too many risks. Ana will never be good enough at this.. you have to work to make your strengths show, and the way Ana has been playing just negates her weapons.