In my experience downhills is much more demading then uphills and, more important , much more dangerous.
You say you find poles completely irrelevant on downhills. Have you tried lengthening the poles to give you the support you often need when on steep/rocky downhill sections?
Hehe, I always get these questions regarding poles. I totally understand they work for most people, and if Eswee had been training with them, I would have probably recommended it, for all terrains.
I told him not too because he is not used to it and it could be 1)extra weight and 2) risky if he learns the wrong technique on the way.
In my case, and that is completely personal, I have tried and trained with poles this entire year, and indeed took them to the Camino Lebaniego. I am quite young (38) and since my childhood, have been hiking and trekking with a 'parkour' style of walking, where I can actually go quite quick downhill kinda 'bouncing' around. As bizarre as it looks, I have very good grip and balance doing that. I do exercise to keep my knees and hips healthy.
Because of that style of walking downhill, the poles actually become a hazard to me, because they add weight, lenght and change the stability of my body.
So, yes. I have tried the pole in many different ways. Even wrote a post for advice earlier in the year. Found out they were really good to help me uphill, but even with the right movements, correct straps, etc etc, they were not working downhill. My husband loves them and says they are totally crucial for his downhill walks, while for me, well, nope.
Hence why it is so important to test gear before you go, and to do on the camino what really works for you. To all those who like poles, yup, they should surely use them