Breaching the Edinburgh wards would be an explanation for the power level.
BUt even that doesn't completely track for me. We've seen Eb many times leave the protection of those wards. He's not some sort of super-hermit who never comes out to the point where the "best" option for getting him is something as complex and powerful as CI. As for Eb's personal power level, I completely agree that he's a magnitude beyond Harry. But, he's still mortal. Presumably he's as vulnerable to a sniper round as Harry is. Kinkaide wasn't afraid to throw down with him, and he's a very risk-averse guy. Also, in the war with the RC, Eb wasn't the main problem for the vamps. Morgan was the one who seemed to be doing the damage. He was the one recognized by Summer for his valor on the field and he was the one who almost took down the Red King. They didn't seem to be having any Eb-centric issues other than Ortega's satellite incident that would indicate that the Red King decided that the entire focus of the Red Court should be directed at removing Eb from the field.
For me, if Eb were the target, there's better and easier ways to accomplish it. Easiest I can think of would be for an up-and-coming RC vamp (similar to what Bianaca was) who wants to make a big splash to go out and get herself a Seal Team. It would be child's play for a gorgeous RC vamp to find on off duty, and turn him. Next up is the rest of his buddies, and bang, she has her own uber-lethal hit squad. Then draw Eb into the field, probably by threatening Harry, and then let the long-range bullets do their work. Afterward, Bianca 2.0 presents Eb's bullet-ventilated head to the Red King and she's on the fast track.
Point being, in my opinion, CI was way overpowered for taking Eb off the board.
If it turns out that the reason for the overkill was to breach Edinburgh, then I'll accept that from Jim since he's at least hinted at that sort of power level being necessary to accomplish the task. I just don't think the narrative of the story has done enough at this point to show that the Red Court was that invested in Eb specifically. To me, the question remains, who were they that invested in destroying, or who wanted the RC out of the picture badly enough and who could have manipulated events sufficiently to bring about the outcome we saw?