I haven't had time to go through enough questions to make up my mind on whether I'm OK with this aspect of the new design or whether I think we should go full blast and change to a serif font, but I do want to note that the problem is at least much better than it used to be - and give credit to the design team for addressing this.
Compare the same example I used in the original request, with the new fonts vs the old ones.
###New CSS
###Old CSS
In the old fonts, the LaTeX tends to stick out like a sore thumb, but it definitely blends in a lot better with the new ones. I'm holding judgement on whether it's enough or not for the moment, though.