(Author here) It varies. Well done on your 9% overall CTR--that's fantastic for a list of 20k. Not all companies are as fortunate to have an audience like that, so for them an increase from practically 0% to 1% is a big deal, even if there's still more room to improve.

I should update the post to include a few more recent examples from other companies, that had higher baseline metrics but still saw improvements from simplifying their emails.