although none of the supplements seem to have any proof, the argument that a good balanced diet is all you need is also flawed i think.
If an ape/monkey gets injured, it will likely die through inability to to feed etc – now although that’s not quite the same for us, the point is that the ape/monkey doesn’t need to focus on curing the injury. Either the injury is life threatening or it isn’t. so the natural diet argument is not tested in any other species apart from humans.
for us, I’d absolutely agree that a balanced diet is perfect for what we need to do – just general living. If we want to engage in physically demanding sports and recover from physical injuries then we might need to focus a bit more on repair to tissues, rather than just maintenance. Plus we want to live active lives way beyond what seem to be the natural lifespan of any comparable creature, so personally i’d like to do anything i can reasonably do to ensure that i’d able to function well into old age.