I definitely think there are two reasons Lansbury is getting so much praise in this production: 1-She's so well-respected that some people seem to just be ready to praise her regardless of what she does, there's nothing Tony-worthy about her performance though, it's a good performance but nothing that calls for the kind of overblown praise she is being given on the board, 2-She actually knows what she is doing unlike a lot of the people sharing the stage with her (not referring to Catherine Z. Jones whom I thought was pretty great) and she manages to rise above the production. Again, even reason 2 is not enough reason to give her a Tony, but clearly I'm in the minority.
And muscle, it's pretty ridiculous to argue that Brooke Shields is more widely known than Catherine Z. Jones. And even if she is internationally famous, the kind of celebrity and prestige that Catherine Z. Jones (an Oscar winner and a true A-lister) can't compare to Shields. Still, I imagine she'd be a likely option (hardly the best) to replace Jones.
"Some people can thrive and bloom living life in a living room, that's perfect for some people of one hundred and five. But I at least gotta try, when I think of all the sights that I gotta see, all the places I gotta play, all the things that I gotta be at"