I think that the problem don't come from your setup or whatelse but because you're using a mouse (as i do). We (mouse drivers) can't modify the brake strength during the braking as wheel's owners does. It's all or nothing and as you all know it's not a way to brake. Reducing the brake strength or balance in your setting can help but here is another idea.
When you come to the braking zone, just hit the brake and don't try to turn. When you reach the top speed limit of the corner, just let the brake off but don't turn yet, just let the car goes. Wait a short moment to stabilize the car then aim for the apex. When you've reached the apex, then accelerate.
I know it's seems stupid and you all know how to do. But the thing i'd like to highlight is not the braking but the dead time between the end of braking and the acceleration. During this short moment, the car will stabilize, the suspension wich were pumped by the braking will release and give you more efficiency. Only wheel's owners can brake until the apex.
This is how i do and it's working pretty well with the tbo's but also with the other cars. I think it's a way to do when you have a mouse. Now try it and see if it's better for you.