This assumes availability of time. Obviously, given enough time, people could develop both top-tier engineering and DS skillsets!
Of course, if lots of free time were common we'd all be full-stack developers who also field sales calls and work on product strategy etc. etc.
/u/dxbydt commented on this very well, so I'll only reinforce the point that not everyone is Donald Knuth. If the distinction between DS and Engineer is blurred in your specific instance, and you're capable of Knuth-ian levels of work in both, you are almost certainly underpaid and need to lead a team or start a company yourself, stat, since a top-tier combination of those skills is exceedingly rare.