On top of what you well said, there's also the fact that many of the voice actors for the Straw Hats weren't hired as unique stars for their characters: Ikue Otani had already played kid Sanji; Chō played two relevant filler characters before Brook (Henzo and Barbarossa); both voices of Jinbe had been working for in the series (Daisuke Gori played movie characters plus Rockstar and Dorry, and Katsuhisa Houki is Moria); and we all know about Kazuki Yao playing Jango and Mr. 2 before Franky. They aren't superstars, just actors doing a job.
As you stated, Hayami seems to be in a different dimension no matter how you look at it; actually reminds me of my country and how One Piece was dubbed here: it was given to a, let's say, smaller studio, probably cheaper, with a few actors doing many different roles (pretty much like the original in this sense). The show itself stopped being dubbed right before Enies Lobby, but later the movies were released in my language. They kept the original cast for the Straw Hats but they hired one of our most popular voice actors for Brook since the series hadn't reached Thriller Bark so he lacked a voice; the feeling was exactly the same as here, as anybody knew that if the series resumed its dubbing at some point the studio wouldn't afford having Brook's actor as a regular, both in terms of fees and availability.
Same here, basically.
