I think we have different definitions of what passing knowledge, and familiarity.

The examples of math knowledge that I provided are taught in the first semester/first couple of semesters of university, and are covered in introductions to calculus. It is 'passing knowledge'.

I think what OP is saying is that folks should leave college knowing how to think and reason mathmatically, philosophically, and scientifically.

Sure, but how would being able to think and reason 'philosophically' (whatever that means) would help, for example, a mathematician, a software developer, or an electronics engineer?
And, again, how would the sort of knowledge that I mentioned be helpful to an average historian?

Also, how much of a STEM curriculum would you be willing to replace with humanities and art courses?

Everyone knows you don't actually learn anything in undergrad

Huh? What? No.
I learned quite a bit at that time in university. This claim is honestly baffling.

OP is just saying that maybe that problem solving should cast a wider net, I think.

What professional problems would humanities courses help STEM specialists solve?

Even a pure mathematician needs to know how to communicate their ideas within their field.

How, and which humanities disciplines would help with that better than practice with communication in the context of engaging in that field which already does train those skills?
It has also been my experience that humanities and art specialists do not communicate better than STEM specialists. Quite the opposite, actually.

EDIT: Also, do you think that the current state of communication in STEM fields in general, and in mathematics environments in particular, is somehow lacking?