What do you mean by "undeniable steep gradient towards extremism" - it was undeniable that more people were becoming extremists via YouTube? I thought that is what we are discussing? Whether YouTube algorithm tries to show you extremism is another question. I am not defending the YouTube algorithm - presumably more extreme things lead to more engagement.
There was undeniable steep gradient towards extremism, how it worked on me in particular is irrelevant. It is a numbers game.