I also found this question intriguing and spent some time researching but, like RpR's linked article, I couldn't find one that specifically addressed the question "is more light always better?" which I think might be better framed as "is there an optimal duration of sun exposure for optimal fruit production?" My conclusion is that there are too many environmental variables to make a general statement and it also varies from plant to plant. One article I read about figs (sorry, didn't copy it) noted that different cultivars had different light requirements.
Many articles stated that too much sun can be detrimental (as those of us who grow tomatoes in hot regions know very well) but beyond that I think it is entirely variable depending on what you're growing
Admittedly, I didn't spend a huge amount of time on this. I think you might need to research each specific tree species and cultivar.
Excellent question
