Well, I think the show did need an ethnic family. In theory, the Fereirra's were spot on. In execution, they were hugely botched and lamentable. The problem with them now (even though some people seem to be numb to their awfulness and have actually started to say the like them? ugh!) is that they have this massive stigma over anything they do. I guess even if they were good, I wouldn't notice. And this Sasha only adds to the problem in my eyes.
I think they show still needs a bigger ethnic mix, though. The silver lining in this situation, however, is that almost any new ethnic family will be shown in a positive light, because they will be automatically compared to this lot. I stand by my opinion that the only character amongst them is Tariq, and he's been ruined since he was absorbed into the family.
The Di Marco's I actually liked. They were a sort of Italian Mafia when they arrived. I think they were probably only really good in my slightly rosa-tinted memory; if I watched the episodes again, they probably weren't great. I have this memory of them as a sort of mafia, but I actually remember the bulk of their time was wasted on Rosa's dull relationships with Jeff Healey and George Palmer, and then that buck-toothed daughter shagging her teacher. They should have equated the Mitchells like-for-like, as their structure is almost identical. But, see, even a bad family in the late-90s would have been good, as the writing was so simply solid.