What is your evidence against it?
It's not up to me to make a positive claim for your pet theory and then tear the claim down. There are several reasons this is so.
First of all, the assumption will always be that I have only presented those points that I have a ready answer for. Second, it takes too much time and effort on my part to research possible reasons for your pet theories. Finally, the burden of proof ultimately rests not on me but on
you.
However, to be sporting, I will cast doubt on the solar fusion theory briefly.
Point 1: Solar fusion theory predicts that a certain number of solar neutrinos will be produced. To date the right number of solar neutrinos have not been observed. Only half of the predicted number have ever been detected.
Point 2: The Sun's output is variable based on the level of electrical and magnetic activity.
Point 3: The corona of the Sun is hotter than the surface of the Sun.
Point 4: Plasma discharge activity, such as Birkeland currents, have been observed in the corona of the sun.
If the Sun is powered exclusively by fusion occurring at or near its core, we should expect more neutrinos. We should not expect the Sun's output to vary based on magnetism. We should furthermore expect that the hottest part of the Sun will be its core, followed by the surface, with the corona the coolest part of the sun. We should not expect to see energetic electrical discharges, such as Birkeland currents, on the Sun.