Thank you theorists for pointing out what concepts follow reality more closely, and everyone for their wonderful ideas. After all of this discussion I believe I can narrow our ideas down to what will likely be more preferable for a fun but somewhat accurate representation of reality.
Option 1 is cyclical light, such as the day/night cycle (Or maybe seasonal changes?). This feature would require a little extra discussion on how exactly it will be implemented in a way that it will fit into the game properly, but is otherwise pretty straight forward.
Option 2: Giving photosynthesis diminishing returns, or capping it as suggested by Nokk and Phenotopian. There are several ways we could go about this, depending on if we decide to change lux from a percentage to a basic value or if we rebalance the patches to no longer have lux above 100%. But overall I think this is something we can try alongside the other options with little difficulty.
Option 3: Make pigmentation effect photosynthesis rates, as suggested by Phrenotopian. This would give photosynthesis additional depth by encouraging players to specialize and adapt to specific environments instead of each environment being identical aside from lux values. It would require a bit of discussion and research however, such as how we want to handle pigmentation (Would membrane color matter or would it be thylakoid only?), costs (Should some pigments be costlier than others?, should changing cell color cost MP?), and values.
These three options are not by any means mutually exclusive, I believe they could each work effectively for our means so don’t assume you need to choose a single option from the list. Unless anyone objects or has further ideas, I believe that these may be our best options for the game.
So from here, I would like to discuss these options in further detail, as well as ensure that everyone agrees with my choice of options.