Change the method to the madness

First off push the players onto heavy combat. Sit down an build a player character NPC. Then make sure each has a way to escape.
Let the players struggle with these challenges. Push the part to TPK fights.
Now when you do run a role play encounter. Only make them important if it moves the story forward.
That way they get fighting, but you get to create a world.
If you create information to defeat your major NPC's drop in once per game. You don't have to make it a you an them. You could make it runes,tomes etc.
Turning to player power level you sound like is high powered.
Perhaps challenge them with an organization to make life very hard.
I also suggest reading DM guide on gameplay. This at it's core a problem you and the player's have to work through. Good luck.