Why would the tiering of the Seraphim matter?
They all have the same level of durability, and none of them have haki.
Unless you're taking attacks from them, which none of the SH that are fighting them has... it doesn't matter if S-Hawk, S-Shark, S-bear or S-Snake is the strongest or weakest.
Unless you want to randomly presume that some of them are just less durable for... I dunno Agenda I guess.