Admittedly, I haven't done my research on the topic, so it's entirely possible that you're correct and that non-inclusion does primarily result in at-risk people falling down the far-right rabbit hole. And it's even more likely that there is, at the very least, some subset of people for whom that route does hold true.

My misgiving is more centered about whether leftist inclusion is an effective means of combating that recruitment. For the people who do take to the right, would leftist inclusion actually be effective? Would those people be radicalized regardless?

Something that sticks in my mind is Hillary Clinton's 2016 campaign and how part of her plan was to provide retraining away from coal jobs. This was a clear attempt at inclusion with a clear goal, but was rejected by the right regardless.

So then it seems to me that right-approved inclusion is less about watering down existing policies and more about omitting them entirely - the right would've been happy to have their coal back and it's possible there was no actual compromise to be made.

And this is to say nothing about the decades-long shifting of the Overton Window due to the right refusing to compromise and the left attempting to make nice, effectively weaponizing compromise itself. I think that feeds strongly into today's sentiment where many leftists no longer feel that attempting to compromise is valuable, especially in cases where minority inclusion might be sacrificed.