Is productivity improvement a hard or soft skill?

Is it better, for example, to consider and analyse hard performance data or approach improvement from a softer, behavioural stand point.

This is definitely not an ‘either …. or’ scenario.  Hard and soft skills are complementary.

When we change elements of a process, a system, a procedure or a specification, we fail unless the result is changed behaviour.

Preferably we make our changes to processes, systems, etc within a changed culture where we expect contributions as to what to change and how to change to come, in part, from those whose behaviour we want to modify.

Change is much more likely to be successful and sustainable when people do it to themselves (or at least contribute to it)  rather than having it imposed externally.

So, if you want to appoint someone to lead change, make sure they have hard skills – so they can diagnose problems and opportunities for change, and soft skills – so they can generate and support the changed behaviours that lead to real improvement.