I do mean an entire day, I basically did it for 12 hours.

Have to find some ways to entertain myself during the pandemic lockdown :).

So I slowly updated a lot of less important accounts/websites to my new email address over the period of 1+ year.

This is what I did for password manager, I migrated each website on a per-use basis. Every time I used a website with a manual password, I replaced it with a generated password. This automatically prioritizes more important websites, which you tend to use more often.

For email, similarly, you migrate to the new email, and you give people the new one gradually too. Eventually anything that's left over will be spam, and that'll actually be your "less-important" secondary address you can give to websites you don't care about.

Published "privacy policies" seem to be a way of preserving opacity. It is nigh impossible, absent litigation discovery, to decipher what the company is actually doing.