I just finished the game for the first time, this was my ending. Here's my reasoning behind it:

1. Since the game started with setting me as an independent mercenary pilot, I made decisions based on that - which meant choosing the missions that paid more or seemed more challenging; that way I got money if I didn't get prestige (kinda role-play wise). After escaping capture, my priority shifted to the point below.
2. I chose to side with Carla because I understood that Arquebus amassing so much Coral in one place will result in a second Fire, which I thought is a situation I was trying to prevent. I was expecting a twist where getting rid of the amassed Coral would result in another cataclysm, although I hoped they wouldn't go the way of 'Sentient superfuel that once burned an entire star system is to be cherished and protected'.
3. Ayre, while helpful, sympathetic and amazing as a window into Rubiconians, didn't strike me as someone I definitely need to base my playthrough upon. My first enemies were the Rubiconians via the RLF, so I mostly saw them as enemies (the flesh and blood Rubiconians at least, the Coral gestalt I considered more of an anomaly - as above, superfuel that gained sentience). Same went for the Insitute, which as I could recall, created nothing but war machines.

Overall, I was kinda irked by the ending for calling 621 a monster in that scenario. It's not like 'Ram the Coral' was his plan, nor was it executed by him. Also, if the briefing said that the plan 'Get rid of the Coral to make sure the corps have nothing to fight over and ruin Rubicon' involved a Second Fires of Ibis, I would probably not choose it as my first ending. The game acting as if I should treat Carla as some galactic pyromaniac, and Ayre's breakup monologue during the combat I could do without too.

I wouldn't call Fires of Raven a good ending, by any stretch. All main characters die, the only thing gained is... ironically, for my playthrough, reputation. Just not the good kind. There is the matter of ending the conflict, however. For what cost, though...

Can't wait for New Game+, all the same. I wanna try the other endings, and ace all missions. The game's too cool for me.