You should try loading over 200 per hand and do 25 yard farmer's as fast as you can while keeping control of the weights, and do multiple sets...You'll change your mind. The added benefits of strengthening the core, back and lower body make it one of the most useful all around exercises.
I used to do them specifically for strength, then I saw some videos of athletes using it for conditioning by lowering the weight and adding speed and sets. Did them after my main lifts and my lungs wanted to burst out of my chest, got better at it after 3-4 weeks so I had to up the weight to challenge myself. Noticed my squat and deadlift progressed much more smoothly, and I was not nearly as tired after going heavy.(85 to 98% of max)
Also saw a difference when just running around playing ball with my buddies, also far less lower back pain.(old injury)
Also felt I recovered better from my squats and deadlifts. There is probably a correlation there but I am not a scientist so maybe it has nothing to do with the farmer's walks.