Sure it counts. He's a top-notch professional. However, even top-notch professionals can only guess at who or what will hit with the buying public. In the end, our opinions count far more, because we're the ones people like Foster are trying to get to buy their product.
Speaking only for myself, there is nothing Katharine has to offer that isn't already on the market from people whose voices and performing skills I like a whole lot more. I'm immune to the other reasons some may be voting for her, a pretty face and a pair of big ones.
Just curious, but who is already on the market that is anything like her, whose music you would buy? As far as the "stage voice", something for show tunes, classics, etc., we haven't really had anyone like that since Bette Midler.
When Katharine is relaxed she has a very smooth alto sound that we haven't seen (heard) since Karen Carpenter. I may not be totally up on who's who in music today, but when I couldn't understand the words enough to sing along, I switched to country music... and yes, I CAN sing.
As far as David Foster goes, yes he has to find someone the public wants to buy and can learn a lot by watching who we vote for week to week. Getting it to sell can be done with creative marketing. Good points though.