So great is the fear, of subordinate evaluation

The Journal reports, link; the City Council has decided to spend $6K on a survey of retired and could retire if they want to, police officers. If done well, the survey should provide some good and perhaps useful data.

As would a similar survey of police officers altogether.
Why not survey every police officer?

If it is understood why retirees need to be asked about morale for example, how can it not be understood why every police officer needs to be asked about their and departmental morale?

There isn't a better indicator of organizational health than morale.  That, and whether there is retaliation against whistleblowers. Every police officer needs to be asked if they can report superordinate incompetence or corruption without retaliation.

A list could be made, of reasons to not broaden the survey.  Added cost for one.  All of those reasons together, pale in comparison to the main reason why not;

(Powerful) people hide (or don't gather) the truth
to avoid the consequences of the truth being known.

If a survey of all cops would suggest they had confidence in their leadership, the leadership would be conducting surveys at the end of every shift.

It really isn't power that corrupts.  It is the opportunity to abuse power without consequence that corrupts, absolutely.

One of the ways powerful people abuse power is to use their power to escape actual, honest accountability;

• they survey part of a group of stake and interest holders rather than all of them

• they will ask only questions, the responses to which, are not likely to be useful in personally identifying incompetent or corrupt, but powerful, supervisors and senior leadership.

It is human nature to yield to temptation.
The greater the temptation, the more likely the surrender.

The key to eliminating incompetence and corruption in politics and public service, is to make them impossibly difficult to hide.

Survey more subordinates, not fewer.