There is a lot of lifting in farm work, though, and lifting is lifting. I garden for a living and am constantly lifting and hauling large sacks of fertilizer, barrels of compost, large shrubs and heavy equipment, loading and unloading the truck, pitching forksful of bark mulch into wheelbarrows, and other such work. I am quite muscular as a result. I also do a lot of tree/shrub pruning with saws that work on the pull stroke, and with bypass pruners that develop a vise-like grip. And, I split and toss firewood, which is a great workout!
Interestingly, I try to minimize the use of muscle in my work, relying a lot on frame and structure to do the real heavy lifting. Conventional muscle plays a role in the initial lift, but when I'm carrying heavy items, it's my frame that is bearing the load, not muscle, which is why I can work long days without tiring, even though I am in my mid-50s.
If I correctly recall some of Ueshiba's history, didn't he do some heavy-duty farming, perhaps even intentionally to add to his physical strength?
Same kind of work as I do. Same age.
I try to minimize the use of muscle as well. Learned many different ways from my father about moving heavy objects without using muscle. Use a lot of what I have learned in Aikido and T'ai chi chuan to move things (or animals) without using muscle.
I imagine that O Sensei got quite muscular through his farming and his Budo training, and he may have even discovered or recognized some of these kind of ways of not using muscles by working on the land.
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.