In retrospect, the launch of Fox marked the beginning of the end for independent stations. But that was far from obvious at the time, since the schedules for most Fox affiliates pretty much looked the same for the first ten years as the stations had looked when they were independent. Really, the only difference was Fox prime time programming instead of a prime time movie. That changed when Fox got NFL rights and started shopping for stronger affiliates.
That said, I agree with you that the proliferation of cable networks played a part -- a huge part, in my opinion. Absent cable, the independent station model of morning and afternoon kid shows, off-network reruns, movies, and sports would likely have lasted until streaming started dominating TV viewing. But with cable, the kids went to Disney, Nick, and Cartoon Network, the off-network reruns were also on multiple cable channels (notably TBS, which had started out as an independent), movies were on even more cable channels, and the regional sports networks outbid local stations for sports rights.
But for those of us who grew up on these stations in the 70s and 80s, it really has been sad to see stations that are fond memories die. Yeah, the call letters remain but they're empty shells of what they once were. You mention the regional status of WXIX in Cincinnati, but there were multiple such stations -- KSTW Tacoma/Seattle was distributed everywhere in Washington state, and KTVT Fort Worth/Dallas was everywhere in Texas and even into Oklahoma, Louisiana, and Arkansas. Indies from NYC and Boston had similar regional status.