I've been asked to help a client get a CSV where each column header is a permission and each row header is the name of a role, and the cells are the level each role has for each permission so they can compare all the roles side by side

You could do a Show Permission Difference and just uncheck 'only show differences' as a start.. Setup /user roles/ show role differences

Brilliant!

There’s a suiteanswers article which has all roles and permissions in that format

The Show Role Differences tool did the trick. The only thing it was missing was inactive roles, which is good enough for now.

I would just mark those roles as active