> But computational complexity is a separate concern from level of abstraction.

It really depends. Abstractions can and often do to otherwise avoidable copies. It's pointless to argue about computational complexity of an algorithm if you don't even notice that an abstraction you're using is adding a performance penalty in the form of running a linear-time algorithm in the hot path, and is even preventing the runtime from optimizing away problematic code.

I would argue that, in practice, they are not completely separate. Too much abstraction makes it hard to tell what the underlying algorithm is. And even if you can figure that out, makes it hard to optimize.