If the problem of free will is to see how freedom fits into the order of nature, then Kant's basic view about the free will problem is that it is insoluble.

I think the contribution people make is not proportionate to their fame or success. In fact, I think the relation is often inverse.

Kant did think he had a moral route back to rational faith in God, for those who need it, and he thought that at some level, we all do need something like it.

I think that both Mill and Sidgwick are great and admirable philosophers, from whom we still have a lot to learn. I would not favor a form of Kantianism (if there is such a form) that treats Mill's or Sidgwick's moral philosophy with disrespect.

Both Kant and Fichte thought of traditions of revealed religion as ways of symbolically (that is, with aesthetic emotional power) thinking about our moral condition. Both thought that religion would become more and not less powerful, emotionally and morally, if the claims of scriptures and religious teachings were taken symbolically rather than literally (whatever 'literally' might mean in the case of claims that are either nonsensical or outdated or historically unsupportable if taken as metaphysical or historical assertions).

We can never prove that we are free or integrate our freedom in any way into our objective conception of the causal order of nature.

We cannot predict the effects of our actions, especially our collective actions over generations or centuries, to use instrumental reasoning toward these big final ends to tell us what we ought to do.