Of course, installing “modesetting” won’t help. As I already wrote, “modesetting” is just another graphics driver like “fglrx” or “radeon”. Since you’re using “radeon” anyway, it doesn’t matter if “modesetting” is installed or not.
The other EE error in xorg’s log was
(EE) Failed to load module "fglrx" (module does not exist, 0)but i’m only using the opensource ATI driver, is that error anything to worry about?
X tries to load “fglrx” first, since it’s usually the best choice. That message is there because you haven’t installed fglrx, so it cannot be loaded.
You don’t have to worry about that message, if “fglrx” is not found/can’t be loaded, “radeon” is used.
If course, depending on your graphics card, “fglrx” might work better for you than “radeon”, so installing it may solve your problem (if it still supports your graphics card, that is 
).