I think 8 posited the best explanation we’re likely to get - her strength in the Force arose as a reaction to Kylo’s Dark Side. Sure, she said that something has ‘always been there’, but any bloodline explanation compounds the coincidence of living next to the Map to Luke and the Millennium Falcon and finding BB-8. Her being a true nobody was the only way that wasn’t entirely laughable on its face.
But coincidences like that have happened in Star Wars before. Remember when Darth Vader captured Darth Vader’s daughter, who sent Darth Vader’s robots on a mission to find Darth Vader’s master, and those robots ended up running into Darth Vader’s son along the way? All without anyone realizing those connections?
Star Wars thrives on coincidences, so I don’t think you should rag on the sequels for it.