I didn't think so. He stood up to both of the Fairie Princesses and their retinues for a good bit of time. If he was weak to them, I think he'd have gotten dissolved a lot quicker.
Harry's logic in that scene was that he was only going down as fast as he was because at his core he is a Genus Locii which is a Nature Spirit, regardless of how augmented he was. Granted Harry is fallible and was far from an expert on that and even at the time said it was just a guess, but he did say it was Obvious that the Ladies had some sort of Edge.
Not only that, but Demonreach was a genius loci, a nature spirit. The fae were intimately connected to nature on a level that no one had ever been able to fully understand. One could probably make an argument that Demonreach was one of the fae, or at least a very close neighbor. Either way, the mantles of the Ladies of Winter and Summer would carry a measure of dominion and power over beings like Demonreach. Clearly they were not sovereign over the guardian spirit, because it was withstanding them. Just as clearly, they had something going for them, because it wasn’t trying to crush them, either.
Now, For every theory that Raphael is Powering Demonreach there is one that he is powering the Outer Gates themselves, so Id say the possibility remains for all parties to be correct: That DR is Angelic AND that a similarity in the Ladies' Natures granted them a measure of Advantage in that context; could be they (and all lynchpins of the Cosmic Defense Scheme) are Angelic in Nature, deep down.
