Rose should be sexy enough to land Herbie [who isn't played by a typically handsome leading man anyway], but the role was originated by Merman who, let's be honest, was even more sexless than Elaine and Bea.
I never saw Merman, but her performance on the cast album was stunning. And I've heard audio of her doing the final scene just before Rose's Turn with Louise.
Arthur Laurents used to say EVERYBODY was better than Ethel. Angela, Tyne, Patti- he said "Ethel didn't understand the part. Ethel was dumb". But I would argue that that "dumbness" (though I don't consider her to be dumb) made Ethel the perfect Rose. There is a tape of the Merm on Gypsy Rose Lee's talk show where they talk about Rose. Ethel says "People say she was a monster. She wasn't a monster! She loved her children. She was a great woman". Ethel played the role as if Rose was right in all her decisions because Ethel thought she was!
Patti imbued the role with lots and lots of actors studio type stuff. "I couldn't have played it before I did because I didn't have the information". Patti gave a nuanced performance and was fantastic. My impression is that Ethel was a steamroller. I think Rose was a steamroller.
As an addendum, I've seen Tyne Daly, Linda Lavin, Rita Moreno, an actress in Providence that I don't remember (circa 1990) and Patti. Patti was by far the best, IMO. Sad to have missed the Merm.