I have auto exposure usually on and when off, the spikes are just waaayy to huge
Well, if you turn off autoexposure, then the camera no longer adjusts to the brightest object in the frame - the sun - and as such it will be way overexposed and dominate the optics. Just like a camera in reality.
You can modify the flare texture to make it more suitable for use without autoexposure, but then it will look wrong if you have autoexposure on. There's no way to make it look the same size in both cases.