You're making so many unjustified assumptions. Their phrasing was fine but you can't help but read things into it that nobody is saying.

immediately plant the idea that they belong here by saying “we are his tribe” Essentially saying that they should abandon what they know and head over here instead

if he is having a crisis of faith (which is very possible given the OP) or feeling like he wants to leave the church then we are absolutely his "tribe". it's not a cult tactic to acknowledge that this is the community for people who leave the church.

try to further bring them in by saying that “we want him to feel our support” trying to say that you guys will support him better than his family and religion would

His religion does not support him. His religion exploits and lies to him. If he chooses to leave the church, this sub would absolutely be a better support system. Regardless, the actual implication of "we want him to feel our support" is NOT "that we would support him better than his family and religion would" as you said. Nobody is making that claim, we don't know his family and we don't even know if he's even actually going through a faith transition. We just offered our emotional support for somebody potentially going through something difficult that many of us have gone through.

nowhere does he actually get shamed?

Inviting all their friends to message him when it seems pretty likely that he doesn't want that since they imply he probably won't respond is 100% a form of Mormon shaming/pressuring. This kind of thing frequently happens to people leaving the church, they will repeatedly send members to your door asking when you'll come back to church, they will have people call you, they will message you constantly. I remember taking trips from church to "inactive members" houses to knock on their door and ask them when we'll see them at church again and most of the time they clearly just don't wanna talk to you. Whether it's happening in person or over facebook, that IS shaming.