Most people here are ignoring the main reason: the writers were just a bunch of baseball loving rat pack fans who took their love of those things maybe a little too far. In the case of baseball, we only had Take Me Out to Holosuite to deal with (which is a great episode–provided you like baseball, I suppose). In the case of the rat pack, we inexplicably got Vic Fontaine who you either love or hate. I wouldn’t hate Vic Fontaine so much myself if they didn’t force him to basically take up the space that Quark’s Bar was supposed to be, and for him to be an integral part of the show so late in the series. And yes, the musical numbers take up too much time, if you ask me.
I don’t think anyone has a problem with bottle episodes. It’s the bottle episodes specifically starring Vic Fontaine which stretches the premise thin to incredulity that I think people–or at least I–have an issue with. Do another Ferengi or Klingon thing if need be. But attaching such sentiment to a character that the show really really wants you to like doesn’t work for me. Again, he’s a love him or hate him character. At least Ezri’s episodes, while shoehorned, made sense for why they needed to be there if they had to have her as a replacement at all. Vic was just an insert the writers specficially wanted for no good reason.