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human
[Supernatural] What power do demons have against angels?

In season four, we learn that Castiel's garrison fought through hell to save Dean, sustaining numerous losses. What can a demon do to kill an angel? At that time, only angel blades could kill angels, and not enough angels had died for those to be in abundance, as we see with Crowley's reign in season ten. We have to assume demons have some sort of advantage over angels, but what is it? How does a demon kill an angel without an angel blade?
gpt
It didn't specifically had to mean losses in terms of dead angel.

We see that people who are send to hell arrive there with bodies so it is possible that angels are unable to enter hell without a meatsuit. Seeing how (at least at the beginning) it was very difficult for angels to find vessels that are from the right bloodline and are willing to consent the losses he mention could have refereed to the lost of precious viable vessels which is something that demons could be able to destroy in a fight against angels.