Re: being fair to Bujold, the woman IS something like 14 years older the Mulgrew.
As for Mulgrew's voice, I think it "improved" the longer she had the role. She stopped "trying to be" the Captain, and just herself shine through Janeway. Her voice matured with experience, that one doesn't have to bark to be heard. A well placed growl... "Lieutenant!" just crawled up from her gut when she was warning B'Elanna not to cooperated with the killer robots in "Prototype" and B'Elanna caught its every nuance.
Her voice is one of the things I truly loved about Janeway, the other was mentioned on another board. She had the most amazing ability to slouch with superb self confidence in the Captain's chair even when the ship was at red alert!