The tricky part is that there’s no way to know who is using pods and who isn’t. You’d be surprised at how many IG accounts do use them.
Thing is, they’re private. You can’t look it up. A small handful of people agree to automatically “engage” with each other’s posts, and the instant engagement is exactly what IG’s algorithm is looking for, as you pointed out.
They’re usually small. 10–12 people per pod seems to be a median number. Small enough to be manageable and avoid detection, but enough to feed the hungry algorithm.