If we are going to use the complex guidelines for other infrageneric ranks, it might be worth mentioning another guideline which as far as I know has only ever been mentioned by staff on the Rufous/Allen’s Hummingbird flag:
I’m not aware of this guideline generally being followed strictly and I don’t think most curators are aware of it. I’m not super familiar with these hummingbirds given I live out of their range, but from what I know of them they seem like a situation where a complex be helpful…
The last point there is related to the reason that Anatidae subfamilies haven’t been implemented despite how useful they’d be.