What you are describing as a background is all part of a "normal" math/CS undergrad education (at least in Germany where I studied). From a level of the mathem

What you are describing as a background is all part of a "normal" math/CS undergrad education (at least in Germany where I studied). From a level of the mathematical difficulty, Elements etc. (but also current-level research papers) are all readable by anyone with a solid understanding of undergraduate mathematics (which is essentially a decent Linear Algebra course, multivariate analysis, a probability course, and a numerical computing course). I think the reason why employers look for candidates with a PhD is that too many people "scrape by" when getting their CS degree -- e.g. they somehow fulfilled the required coursework, and somehow got their degree. The PhD requirement is essentially a bureaucratic substitute for answering the question "has this person understood math in sufficient depth to be able to do independent work with it".