Did they say that with a straight face? I can't believe that would be serious advice! "You literally need to contact everyone in your address book and make sure they have the right settings."
You're wrong, and the comment you replied to is right. According to Apple, it can take up to 45 days to receive text messages from Apple products after you turn iMessage off.
This was the experience of the person who initiated the class action suit:
"21. Apple personnel informed Plaintiff that even though she had turned iMessage off in her old iPhone she may still not be receiving all her text messages because some texters using Apple devices may not be using the latest Apple iOS version. Rather than Apple coming up with a solution to a problem created by Apple, Apple's representative instead suggested to Plaintiff that Plaintiff get her text message senders to update their Apple iOS to the latest version, or have them delete and then re-add Plaintiff as their contact, or have Plaintiff and these unsuccessful Apple texters start a new text conversation with Plaintiff."
the problem that really exists with iMessage is that it's easy to enroll but people forget to unenroll when they move their number away from iPhone.