What's up with Frostbite Mountains enemy levels?

Ah, Ok, that is disappointing, I thought that Trespasser was the only one that must take place after killing Cory

I usually do JoH after completing What Pride Had Wrought, but with respect to plot, it makes more sense to do after defeating Cory.

That's the one in the Deep Roads, I'll give it a try then
thnx

To be honest I would play all the DLC after defeating Corypheus. It is slightly annoying when some dialogue doesn't seem to acknowledge it but that is a small price to pay.

There is no justification storywise for why you would go racing off into the Frostback Basin to investigate the fate of the first Inquisitor before the immediate threat of Cory has been dealt with and it does explain nicely what you might have been doing in the 2 years from defeating him until the Exalted Council.

Whilst there is a slightly greater justification for doing the Descent before defeating him, there is still no real connection with Cory, only the Breach, which you closed early on in DAI, so the disturbances relating to it again make more sense after he has opened it a second time.

Also, I find that if I have already done the majority of the content in the main game then I am already too overpowered for Corypheus at the end. If you take him on after the two DLC then he is going to be ridiculously easy. So the only real reason to do them first is if you particularly want Solas with you, not that his presence adds a great deal to either story.

It does take FOREVER to bring down that alpha, though fortunately the other ogres you encounter are less of hit point sponges.

One suggestion: try Cleansing Runes. I don't know if they programmed them to work against darkspawn in The Descent, but they do extra damage to Blighted creatures.