This “ads as posts” thing was one of my two biggest concerns with Threads federation. I really hoped I would turn out to be wrong about it, but at the end of the day, both Facebook itself, as well as big social media influencers, rely on advertising for their profits. For anybody looking to avoid ads on Lemmy, it seems like direct federation with Threads is not a good idea currently. On lemm.ee, “no advertising” has been one of our 4 core instance rules from the start.
My other major concern was Threads having the ability to enforce their feed algorithms on federated instances through sheer number of votes on things they show in their feeds, but judging by what you’re saying about the engagement, at least that concern has not materialized (at least yet).