Replying to my own post because it's too late to edit.

This post has clearly struck a nerve as I think it's my most upvoted post on HN ever. Behind this post is 3 companies worth of experience working with great designers (really, UXers) who vehemently advocate on behalf of the user but don't realize their own limitations to understand that user (and to therefore tone down the advocacy accordingly.)

This is particularly obvious in the business setting where truly empathizing with the user requires understanding the business they are in and their realities/pressures, not just their experience in a specific program. The UX'ers over index on what they can infer about the user experience in the absence of that broader understanding - and usually the founders/sales/whoever instinct about what's actually good or bad is valuable to at least unpack because it's grounded in some business/industry/customer intuition the UXer likely doesn't have access too.

I take from the high upvotes of this comment that this is a very common perception, that almost all UXers are oblivious to.