I am really not sure where you get any of these ideas. For each of your critiques, there are not only discussions, but taxonomies of compendiums of discussions about the topics at hand on LessWrong, which can easily be found by Googling any keyword or phrase in your comment.
On "considering what should be the baseline assumption":
On the critique that rationalists are blind to the fact that "reason isn't the only thing that's important", generously reworded as "reason has to be grounded in a set of human values", some of the most philosophically coherent stuff I see on the internet is from LW:
Looking it the first link https://www.lesswrong.com/w/epistemology - it has frankly a comically shallow description of the topic, same with https://www.lesswrong.com/w/priors. In just about every discussion, I may be just the entirely wrong audience, but to me they don't even begin to address the narrow topic of choice, let alone form competent building blocks to form any solid world view.
I support anyone trying to form rational pictures of the universe and humanity. If the LessWrong community approach seems to make sense and is enriching to your understanding of the world then I am happy for you. But, every time I try to take a serious delve into LessWrong, and I have done it multiple times over the years, it sets off my cult/scam alerts.
On "considering what should be the baseline assumption":
https://www.lesswrong.com/w/epistemology
https://www.lesswrong.com/w/priors, particularly https://www.lesswrong.com/posts/hNqte2p48nqKux3wS/trapped-pr...
On the idea that "rationalists think that they can just apply rationality infinitely to everything":
https://www.lesswrong.com/w/bounded-rationality
On the critique that rationalists are blind to the fact that "reason isn't the only thing that's important", generously reworded as "reason has to be grounded in a set of human values", some of the most philosophically coherent stuff I see on the internet is from LW:
https://www.lesswrong.com/w/metaethics-sequence
https://www.lesswrong.com/w/human-values
On "systematically plan to validate":
https://www.lesswrong.com/w/rationality-verification
https://www.lesswrong.com/w/making-beliefs-pay-rent
On "what could hold true for one moment could easily shift":
https://www.lesswrong.com/w/black-swans
https://www.lesswrong.com/w/distributional-shifts
https://www.lesswrong.com/w/forecasting-and-prediction