I think someone else has pointed out that they're not ActiveRecord queries, but even if they were, this is a script designed to be run manually a few times a we

I think someone else has pointed out that they're not ActiveRecord queries, but even if they were, this is a script designed to be run manually a few times a week, which takes maybe a minute. You'd need significantly more than 100x performance increase for any time at all put into optimising queries to pay for themselves.