I saw her last week too. She was very good (I never saw Sarah) but I just think the part itself is very forced. Marin was great in Ragtime and Kiss Me, Kate both parts were very demanding and in Kate, especially, she had high voice and comedy demands which in my opinion, she handled beautifully.
The Lady of the Lake is really not necessary after "Find your Grail" so her appearance in the production number as well as the "Diva's lament" just feel very forced. This is clearly a case of "we have a great singer girl, now what do we do with her?". I think this part was great for someone who is breaking into the Broadway leading/featured actress category, but seems way too smallish for an established leading lady like Mazzie.
The meat is always leaner on somebody else's dinner plate!