I have to agree with OP on this. In a single run of all three dungeons. I had the hardest time with Sastasha HM, and only because of that first boss, mainly because my party was running a BLM and BRD, so no real stunning power besides me, who kept getting stunned despite doing my best to run from the boss when needed. Wiped on the fight, like, three times before we got lucky enough to get its HP down to 0.

Though honestly? I don't think anyone one-shot that dungeon on their very first time. Even getting lucky enough to get past the first boss, that second boss had a very hard-to-predict left-field ending that is practically impossible to fend off unless you know that it's coming. I won't spoil it for those who haven't run it yet, but yeah.

Only problem I had with Snowcloak was the mechanics of the Yeti boss, but we figured that out real quick.

Had no real problem with Qarn at all.

Sas HM was a trial, still oblivious to how the tank mechanics worked for the first boss, but we eventually got through it. But I can say that it was a much more trying experience than Snowcloak and Qarn HM. Not impossible, but trying.