About 1-trick pony's
I do not agree that Arsael is 1-trick pony.
I think it is more about need and imagination of current Companion. Arsael actually has her own sword (Scene at start). And enhancement too. It is more option in combat and potential to parry melee attacks. Parry is skill that need to be learned. Also Arsael can hover in open sky, that alone gives more 3d mobility potential to her Companion than Dia. More space for dodge and counterstrikes. They are skills to Companion learn too, Arsaels responsible only in speed and power there. And Arsael has plenty combat experience of all kinds, and can assist in training. As Eda did to MC. Yes, Arsa has only basic regeneration and can't properly heal or shield in combat. But, i'm sure, she can set explosive mines (she did set at least one in HighOrder truck, if you remember), firebelts (webs of mines), firewalls, rains of fire (series of explosions in exact order and places). All sorts of things to set ablaze everything around in continuum. Zero said as much, i think. So, no, Arsael's Companion can smoke even skilled opponents. She is 4th Primordial. Just her Companion need to more proper training, experience and learn about Arsael's capabilities. Zero was disappointed exactly for that reason. Emma did not used even drop of Arsael's true potential. Overpowered slapping around from spot, staying still whole time, it is kinda meh. Not really Arsael, not really fight.
Yes, i do love Arsael, and want her to more shine. I want Emma to accept Arsael truly. I want properly trained and experienced Emma challenged in decent combat. Heh, we ll see.
Amy seems to can transfer her healing to others, to certain extent, so i guess, it will be actually Amy who heals Emma. And also, i guess, at some point, she will capable to regenerate instantly or mb even grow doubles bodies on the spot from separated parts. Need to learn how her transfer and bond works more too. Only guesses here. She is just newborn Darkone, at the moment, i'm sure dev shows us more in future.
As for Cia, (1) perception surroundings, (2)learning enhancement and (3)mind reading it is obviously not 1 trick, and that is pretty big. She is A rank. So its enough for her. She is fine. Good and enough for A rank.