Show has made a few mistakes but it's pretty much on point. Yeah the whole dorne shit was terrible but look at the source and the tv constraints. Dorne characters in the book are also shit filler, they were brought in only as a segue to fake Aegon's conquest (which is itself more shit filler), it exists only as a method to achieve the demise of the rest of cersei's children before her own death per the prophecy. Just shit that happens that makes westeros utter shit so the white walker invasion can happen unopposed until dany the messiah arrives.
They opted to parse down the shit filler to things the audience is already familiar with, so no fake aegon story. but Cersei's fall, her children's deaths etc all still need to happen, it still needs to involve dorne, and they also are just coming off a season with a well received dornish character in Oberon so, it made sense to bring dorne in now and use it to setup cersei's fall.
Selmy, shireen, etc is just the show spoiling the book, not sure why the fuck people are butthurt, "omg hasn't happened in the books" YET. Show has been spoiling the book since season 4. get over it.