We have looked into this and the main issue is the definition of critical workers is very narrow (Criteria for long term critical workers):
Of note, the criteria mostly relates to the delivery or execution of:
a government-approved event, or
major government-approved programme, or
approved major infrastructure project.
There is a list of the approved projects here (mostly government infrastructure project):
So if this is a line of work you wish to pursue, I would suggest contacting the companies that are working on these projects to see if they need any help, or how they are getting on with INZ and getting people into NZ on these.
This is a big issue with many companies struggling to find staff in certain roles, e.g. IT roles, but the current INZ rules do not help with most of these type of roles.