Pragmatist strictly fits better since it's the distinction of whether one is simply realistic, as in an individual who has a firm grasp on reality and operates on facts, whereas someone who is pragmatic is practical. Something like "go kill the hero when he's a kid" is not a fact-based world view, it's a practical decision based on factual information; all pragmatists are realists, but not all realists are pragmatists.
That said, it's a moot point since the title uses リアリスト for "Realist", though the chapter-by-chapter translations might be somewhat less chunky if they occasionally subbed out the term.