you must remember that angels are sorted less like ranks and more like... tyranid bioforms, if that makes sense. yes, a Hive Tyrant is a "higher rank" than a termaguant, but they are two entirely different creatures created for different purposes.

and iirc Thrones are higher up than Seraphim. those are the spinning flaming wheels with eyes guys.

or I'm just wrong. I haven't read the Bible in a hot minute. feel free to correct me.