What I think you are talking about (please correct me if I'm wrong) is the weapons ban placed on Okinawa by the Japanese. But from what I have read in more recent years, that ban was actually rather loosely enforced. I find the idea of someone from the Okinawan warrior class being inspired to create a weapon based on the tools that farmers around him used to be far more plausible than farmers developing systems to use their tools as weapons. The first reason for this is that in most cases farm tools are not designed to be used as weapons. For example, a farmer's sickle (kama) has to be thin and light in order to be useful, otherwise your arm would get tired before the crops were in. Where as a sickle (kama) used as a weapon need to be heavy, both in the blade and in the handle.
I do agree with your idea that the more physical lifestyle of the past kept people in better condition than the modern lifestyle does. But I think for teh rst of your theory to hold up, we need to have some examplhistorical evidence (i.e. written histories of Japan/Okinawa) shows that the average joe wasn't really able to defend him or herself against the warrior class.
Finding a link between using gardening tools and weapons may be useful to you, and I see nothing wrong with it, that said, while a farmer's (or your) experience clearing land allowed you to efficiently cut bamboo, it doesn't translate to the combat use of a weapon. Remember that test cutting was intended to test the blade, not the swordsman. While there are things that a swordsman can learn about his cut from test cutting, it is not the primary focus of sword schools, and you see very little of it in the koryu. mastering distance and timing are far more important from a combat standpoint. For my money, I would be more afraid of the butcher, who has experience seperating meat from bone, than a farmer.