I actually found the graphic gore rather inappropriate. Presumably both the time slot and the subject matter, not to mention the inclusion of young Bruce and young Selina as main characters, means there will be children watching. But the gore here was R-rated stuff, or would've been a decade or two ago. I did not enjoy seeing that and I don't think it was necessary for the story.
Your criticism reminds me of the stories of people who took small children to see The Dark Knight, thinking that because it was a Batman film it was appropriate for them. It wasn't, and if the parents had done a modicum of research -- or even read the bloody poster and its MPAA descriptor -- they'd have known that. Gotham is a TV-14 show. I'm not sure it really belongs in an 8 pm slot, but they do have a content announcement before it starts, so audiences can't say they didn't know what they were getting into.
I went to see Gone Girl this past weekend with my wife and someone had brought two kids. Yeah, that's not appropriate.
As you say, the TV-14 is enough of a warning for anyone with any sense. People with no sense cannot be helped.