Hmm, I noticed the lack of overweight MCs more than the lack of PoCs when I was growing up...probably because I was all chubby and weight was always an issue. It was only after I moved from Asia that race became a more prominent issue for me, and that's when I started noticing the lack of PoC in popular media.
This is still true. And if a character in a novel is heavy, you can almost guarantee that he or she will be portrayed as either villainous or comical in some way, or that (if a sympathetic character), he or she will lose weight as part of undergoing an "ugly duckling" transformation by the end of the story.
To my shame, I realized that in the first draft of my novel, the only person whom I described as being heavy was an unsympathetic character. And while I was pretty slim as a kid and young adult, I'm definitely fighting the "battle of the bulge" in middle age. I mean, yes, I'm evil. But I was before I gained 30 pounds too.
I think some of it's because most people in North America and Europe who are overweight fantasize about losing weight, so that story arc is a sort of wish fulfillment, and fat is seen as the enemy. Still, it would be nice to see more sympathetic, lovable characters who happen to be heavy and stay that way.
I'm white, so I never had the issue of noticing that most protagonists were of a different race from myself. I do remember some stories I really loved that had characters from different cultures, religions and ethnicities, though. I think, in hindsight, my mom made a concerted effort to find books for us that portrayed people from different cultures as sympathetic with as few stereotypes as possible. But the overwhelming majority of books still had and have white characters.
The biggest thing I recall from my childhood and young adulthood (and I know, it's a tiny violin) was the way blue or green eyed blondness was portrayed as the pinnacle of white beauty (I have dark hair and eyes). It was oh so rare for heroines in stories to have hair and eyes that were both dark. That bugged me.
I'd guess that this is even more galling for people who aren't white.