Well, let's face it- the acting on the show isn't great in general
Except for Goodman and Metcalf, who are both genuinely good actors, the cast was typical sitcom quality and Roseanne herself was often distractingly inept at delivering her lines. But this and some of the contrived sitom-y contrived plotting you're mentioning just sorta comes w/ the territory. I mean, it's often lauded for being groundbreaking and it was but in a lot of ways it was still a traditional sitcom. It certainly didn't throw out the rule book like "Seinfeld" as some folks would have you believe. But within the parameters of the traditional sitcom format- dysfunctional family's trials and adventures and all the milestones that entails- it managed to be darker and funnier than most sitcoms could ever dream of being.
As far as villain characters are concerned, at least they had good ones, for the most part, like Martin Mull's Leon.
I'm admittedly out of touch when it comes to modern sitcoms and the types of jokes contained within (though from bits and pieces it seems like they're getting less and less realistic- characters all talk like comedy writers trying to shoehorn zingers into everyday conversation rather than like real people)- just had trouble imagining a character on something like "Modern Family" using the toaster line. And yes, though "Roseanne" took it to the extreme, sitcoms were generally more mean-spirited during the 90's then they are today