I think we're omnivores too, nor do I think meat is a curse, but as it's suggested in religious texts, "for times of famine". And from my own personal experience I can say that I understand why this is recommended.
So have you eaten a raw plant food diet for a long enough period of time to fully experience it? I have and I can tell you what foods cause my body to remove mucus and which ones create mucus. I can also tell you what foods make my vision blurry and which ones make it clear. Or which foods make my joints and bones hurt and which ones make me feel good. I was born with the inability to breath through my nose at 100%, it was more like 10% and I ALWAYS had one nostril plugged up. Guess what changed that......the foods I quit eating.
We can put Pottenger aside and disregard it simply because they're cats. I doubted all this too, but I eventually told myself...."how can I really know, unless I put in the commitment to fully experience it for a few months." But I can see the Pottenger study reflected in other species, namely the only species on the planet that cooks it's food or makes, "food ingredients", in a lab.
All I'm trying to do here is offer a suggestion to the OP of my own personal experience in what has helped me feel better. The OP didn't say her knees hurt after one ride, it was said that over time they began to ache....and that in her family there's a history of knee issues. So I commented on what I felt could be of benefit, and I can't be convinced that my own personal experience is false.
If processed food works for some that's fine. But for me it doesn't work and it makes me feel terrible. The generations before me ate more and more processed food with less and less nutrition and that lack of good nutrition was passed onto me so I had to figure out how to feel better without destroying my body via more and more chemicals the doctors wanted me to take to just cover up my symptoms. And that lead me to what I'm trying to share with the OP. Eating good makes me feel good.
And everyone else was commenting on riding technique, so I commented on something that I felt was also important and in my experience makes a difference.