Most of those shows AREN'T marketed towards teenagers. LOTGH is specifically for a 30+ crowd in both marketing and audience. Planetes is a seinan manga and was pointed specifically at a college or older audience. So was HaiRen, Shin-Chan, and Tatami Galaxy. They're all intended for the 30ish audience, and none of them are violent. Cowboy Bebop and Berserk are the only ones, really. With the exception of a handful of shounen or horror shows, most popular anime don't fall into a particularly violent category.

But I also disagree that we don't have a demand for it here from the domestic market. There's a reason things like Spawn and X-Men are fondly remembered. There's a reason X-Men Evolution and Avatar gained a lot of traction and have still-active fanbases today. When shows of a decent to good quality come out that are thematically more complex than your average gag cartoon, they get invested fanbases.

I don't think Japan is filling some void with anime, certainly not pigeonholed as violent the way you've stated. What IS incredibly true -- speaking as someone who works in film and television and has seen incredible pushback against mature animation -- is that our industry is dominated by an attitude that cartoons are for children, and that's the only crowd you can sell to.