Does the ad group still mean anything as a unit of control under smart bidding?

Trying to build a mental model rather than follow advice, so bear with the length. Under manual bidding the ad group was a real unit of control: you set a bid there, you adjusted it, and the structure of the account was also the structure of your bidding. Under target CPA or target ROAS the bid is decided per auction on signals I can't see, and the target sits at campaign level anyway. So what is the ad group actually for now? The honest answers I can come up with: - It decides which creative can serve against which queries. - It's a reporting bucket. - It is a level you can attach negatives to. None of those are bidding. Which makes me wonder whether the way most of us structure accounts is a fossil of manual bidding that we keep because it is familiar and because every guide written before 2022 assumes it. Has anyone deliberately restructured around what still has levers on it rather than around the ones that have gone? Interested in what that looks like in practice, not in theory.