Nancy may not be the central character of the show, but it really is a fantastic part - in terms of meat it is far better than Maria (pretty wet) or Joseph (wetter still). True, she doesn't appear for at least an hour, but when she does, she launches straight through 2 production numbers (It's a Fine Life, and I'd Do Anything), and she holds act 2 together no doubt (including the huge ALAHNM, twice). Oliver! is not the star vehicle that Hello, Dolly or Funny Girl is (and there are loads more: Sweet Charity, Evita, Gypsy...) but the part is not "a walk in the park" if done well.
As for 6 shows a week, I agree with you, it is a disgrace. Hopefully, this is just covering backs, and Jodie will play at all performances once she proves herself able. However, if she can't do it, then the whole casting process is ridiculous: if so many people auditioned, why put unsuitable people in a position where they could win? Also, whoever says that Mr. Joe Public shouldn't buy tickets just to see Jodie has missed the point of the exercise: you create hype by casting a star, but you also create the star. The show sold over £3million in tickets during the first week of sales - this was nothing to do with Rowan Atkinson - simply because people want to see the IDA winner. If the producers were planning on a six performace schedule for the winner they should have said so at the time. If I had booked for Wed or Thu I would be very angry at this jucture.