How is my stating that all characters have the potential to be interesting "acting like the show is new or something"? I honestly don't get that correlation at all.
And so the writers have tried with Meg, Chris and Lois before; their (alleged) lack of success doesn't automatically mean that said characters just aren't any good, but that the writers didn't try hard enough, or that maybe they need to bring in some different writers.
Most characters evolve. Bugs Bunny started out one way, then over the years, he evolved into something else. When Disney was producing theatrical shorts, they didn't want to do a lot with Scrooge McDuck, because they felt at the time that a character whose sole motivation was to go wild over money wasn't interesting enough to carry an animated cartoon; Carl Barks and the producers of DuckTales have greatly disproven this notion. Few characters end up exactly the same way they started. Stewie started out as an infant version of a Bond villain, not the effeminate weirdo that he is is now. Peter was originally more or less an idiot Archie Bunker; he too underwent an evolution. Peter, Brian and Stewie aren't innately superior characters to Lois, Meg and Chris; they've merely become favorites of the writers. It's like what happened with Butters on South Park; he went from being an extra on the show to one of its' top players, because Trey Parker took an interest in him and began to evolve him, running with the character as often as possible. If one of the FG writers took that same interest in the other Griffin family members, give them tons of cutaways, have them break the 4th wall, etc., they could likewise emerge as top players.
As a writer, I refuse to accept the notion that some characters are just innately uninteresting. To me, that's just fanboy-perpetuated BS and an excuse for laziness on the part of writers. We'll just have to agree to disagree there.