I don't think their careers at this point are comparable even slightly... not even slightly. Other than "rising star who is established in some way".
And more importantly their vocal ability, as we currently understand it, isn't even in the same world. I don't think Funny Girl is funny or good enough as a play (including lyrics, meaning they aren't that funny) for the show to succeed based on a funny person playing Fanny if they can't wow with the vocals. (I also think the show deflates if the Fanny can only sing but isn't funny).