You can't help what is or isn't mainstream, someone's always going to be unhappy or left out by that. There's going to be people like you who want less brutality, and those excited for more violence. But you can definitely pick which levels of violence in Batman stories you are exposed to. If you've seen the Lego DTV movies, you can try the two Adam West movies (they're great), or the Scooby Doo crossover (brought back the Brave and the Bold Batman), the TMNT crossover (PG 13, and the most violent thing I think the Turtles have been in for the past 20+ years, but that's mostly just Shredder and R'as being killer ninjas), the three Batman Unlimited movies, Batman Ninja I don't remember being that violent. And you can always rewatch the cartoon series like Brave and the Bold or Beware the Batman.
And for the comics, I recommend checking out the YA and Kids OGN lines (Batman Overdrive, Nightwalker). They recently brought back the DCAU Batman in an ongoing too.
Again, if it's the mainstream perception of Batman that worries you, you'll just have to learn to accept it and move on. But if it's just what you personally are tired of seeing, there's a lot of stuff that I really think you should check out. I mean I think it's every Batfan's civic duty to check out Adam West's last work on the character he helped make a pop culture phenomenon for decades.
Once upon a time he was a character primarily meant for kids, but that hasn't been true in over 30 years, especially moreso now. That doesn't make him a character primarily meant for adults either. He's reached the point for a long time now where he's primarily meant for everyone. There should be more brutal versions meant for an adult audience. There should be more wacky, funny versions meant for little kids. There should be versions in between the two meant for everyone. And now, for the large part, there are all those versions.My feelings about it are complicated, because I think this film overall looks extremely well put together and has a lot of promise so I'm willing to see where it goes. But we have more than enough Batman films in general and I find the pushing of the heightened violence with Batman to be inherently distasteful since he's a character primarily meant for kids to view as a hero. So I'm basically at "we really don't need this, but this specific thing still looks cool and it could execute its ideas well so I'm interested."
Besides, it's easy for us older fans to get into a bubble and think that the versions we're most exposed to are how every audience is exposed to him, but that's not true. Most kids aren't going to be allowed to play the more violent videogames until they're teens (depending on what their parents decide). Parents won't take them to see R-rated movies if they don't feel ready for it. The version occasionally seen on Teen Titans Go is the version most kids you're worried about are going to see. I mean Teen Titans Go is admittedly a kind of violence being perpetrated on our young, but that's a different discussion...