>>riidom+(OP)
The advice is, in essence, to prioritize your mailing list over audiences on proprietary platforms like Twitter and TikTok. This may work for some, but mailing lists seem like they would be really ineffective for a lot of use cases.
>>rp1+84
The advice is more generalizable than that: move your audience into content in spaces that you own -- not spaces that Zuckbook or Google or TikTok own.
>>setpat+X9
I don't think the advice is the move your audience to spaces you own. The advice is to move your audience to spaces you own that intersect with spaces they go often. E.g. moving users into a forum you run wouldn't work because it would require your users to explicitly go to your forum. Mailing lists work because people go to their email inboxes often. I'm struggling to think of another place people go often that isn't a proprietary platform.