I’m not a fan of bots ripping content from Reddit. But these would be humans.

The content on Reddit is also submitted by humans (well, mostly).

You would just be adding a thread inclusive of replies. Unlike bots, toot authors also reply.

This assumes that a post pulled from Mastodon to Lemmy will also push comments from Lemmy back to Mastodon (or at least notifications of comments)… which is a real infrastructure problem, and also depends on the Mastodon communities wanting that interaction, and the admins allowing it.