A few thoughts here:

A reader might get the impression that Johnson was well-suited for the GG role because he was a constitutional law scholar.

I dont think that's the case. Johnson was was well-suited because he was Johnson, ie his general temperment and enthousiasm. https://twitter.com/nationalpost/status/1287411741580840961

We've had a situation where an SCC justice acting as Deputy GGs caused momentary panic in part owing to their status as legal luminaires, ie questioning whether they should be granting royal assent to a bill.

Constitutional law is a wide field and we wouldnt be well-served by a Charter expert raising questions about legislation that requires assent, for example.

Same for political scientists with expertise in the Crown. They might spend way too much time excersing their Bagehotian rights to caution, warn, and be consulted. Or at least more time doing that than a first minister would be comfortable with.

Put differently, I'd argue judges and academics would be bad fits for the role, generally speaking.

As Johnson shows, the exception would be university administrators. That's the kind of job that can prime you to be a viceregal (lots of speeches, troublesome profs/ministers).

This may be why Australia appoints lots of former military flag officers. Theyre used to protocol, lots of speeches, dealing with crises with authority and a cool head. They spend decades training to be a leader.

(On the last point, yes training to be a leader matters. It's not just about charisma, it's learning how to treat people with dignity and respect, how to motivate them, how to handle problems smartly.)

(As an academic, where people often have to learn leadership on the fly, it's stunning when you work with someone who has *decades* of leadership training.)

Back to the main point: I'm sure there are other sectors that provide this kind of formation. Maybe the charitable sector, upper echelons of the civil service, diplomats, etc, etc.

Traits to avoid: contrarianism, risk taking, partisanship, stubborness, etc.

Those may be great to head govts, but not to head states.

Finally, is this a gender thing? Nope.

Some of our best recent LGs, such as the current LG of Ontario, have been women.

Real finally: the point is these positions are about judgement and demeanor rather than specific knowledge.