Not sure Radiohead qualifies as mainstream - they may get played on MTV,  but I've never noticed them as heavy rotation, and the Amnesiac tour dates were spread so each venue covered 5 states - I saw so many out of state plates, I thought I was at Cedar Point!   When you listen to anything past OK Computer, it takes some work to really get into it, and there's a large percentage of the aduience that won't listen to anything they can't grasp immediately.

 As for Tool, Maynard's more political / conspiracy minded statments can be dissmisssed as more sci-fi ramblings for headbangers in a style that has a long history of fictional excess.  He kinda slips it in under the radar.  Considering the simplicity of most metal, I'm suprised he's as successful as he is serving up the dense textural stuff in Tool - But he's always had a good pronounced bass line that you can grab on to grounding things.