I don't think people are feeling this way because of who's writing and the writer, in my opinion wouldn't change a thing about it for me. I personally feel that Peter's past, origin and history is all fine. He doesn't need any "long lost" relatives. Part of his character has been about how he's been alone, May being his only family to hold onto.
Weird, but I actually kind of like the idea of him having a sister. I imagine her being kind of like Ultimate Spiderwoman. I'm hoping she doesn't have powers though.
This reminds me of a very old comedy where the hero discovers he has 4 twin brothers. And every time a new brother is revealed his mother starts crying "Im soooorryyy! I meant to tell you a long time agoooo!" that's what Aunt May is going to do.
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Azula: My mommy didn't love me so I'm going to burn down your village.