I do not see however how one could learn these things by just lifting weights - it seems like a rather one-sided training regime in contrast to the many different ways muscles are being used in farming..
On the other hand, I can see how some weight lifting exercises could help to overcome certain physical problems.
I agree... if one just lifts weights, one learns only how to lift weights. When we're doing physical labor of the different kinds described earlier, there are other factors involved, including changes in the terrain, shifting of weight/mass in the loads being carried, etc. We develop the proprioception needed to make the necessary changes in our bodies to accommodate the changes in the environment around us and in the nature of the different work we are doing.
Weight lifting has the specific purpose of building muscular strength and bulk, and increasing bone density. It's not a secret that even very elderly people can benefit significantly from an appropriate level of weight training.