one could technically add a group which revokes all privileges associated with editor/autoreview

See: https://www.mediawiki.org/wiki/Manual:$wgRevokePermissions

Ultimately, both way to implement this have upsides and downsides.
If one would like to be able to make exceptions to this rule while keeping the group membership meaningful, disabling autopromoting would be better.
By contrast, the revoke approach could allow to revoke additional permissions (e.g. editsemiprotected), while keeping others in place (e.g. rollback), if this is desired.

Actually, I would be more happy to stop autopromotion for accounts in a certain category (per wiki, configured via system message) since that needs no maintenance efforts.

For a group solution, we would need to evaluate template transclusions or category every two or three weeks and each fresh account will be assigned to paidediting group by sysop. Then autopromotion could consider this group. That needs permanent human analysis and operation. However, a group paidediting would be pretty for evaluation by tools, and is visible on edit analysis, e.g. by xtools.