Adding my 2c
I enjoyed the B scenarios as I found most of them quite challenging for my erstwhile heroes. All but one of the B scenarios had to be played 3-4 times to get through and the one scenario I did get past first try, I felt was more luck based than deserving.
However I recognize that I am an outlier in your customer base. I've been played conflict sims (wargames to most of you) since I was 8. I revel in complexity and challenge.
To most players, such abject failure to progress would be highly discouraging.
Further, I call to question the blog post above. If AD1 was meant to be overwhelming for your characters, why were the B scenarios that much harder than them?
With a sense of relief I found that the ultra scary demons of the Fall of Kenebrae needed to only be faced, not defeated. I thanked all the gods whom would listen that the AD1 cards had lessened the chance of pulling Arboreal Blight, or that the servitor Demon summoned by Demonic Hordes for this set was easier to deal with for most of my characters than what we had faced earlier.
I don't believe for an instant that this was the design intent. A sense of relief while playing scenarios representing infernal hordes overrunning the world?
So as an avid gamer and someone whom has helped design and play test a myriad of systems some constructive comments to soften my negativity
There is nothing wrong with banes that will push the party to the edge. But the frequency of such challenges must be carefully considered. Something you can consider for the future is a phased deployment of such banes. If Arboreal Blight (for example) had one copy in each of sets 1, 2, & 3 I don't believe you would be seeing such a level of dismay.
Carrion Golems 3 appearances in the base set + add on also makes life 'interesting' for spell casters. My party may well be less effected than most, with only Kyra and Seoni vulnerable to such depredations, while Balazar fares quite well against it. But when it does come up for them it's either a hand wipe or a bunch of party blessings used up. I think the latter is the intent, the former not so much. The trouble with such a bane is that the immunities are so arbitrary that there is no feeling of challenge. If force for example worked, canny casters might be able to hold something back for this guy. But there is nothing in their arsenal to take this thing on. So while Alain charges this thing down with gleeful abandon, other 'equal' characters are quaking in their boots (or sandals)
I realize that the design space is limited by the RPG's adventure path material, But simple "Got Ya"s such as this seem arbitrary and forced. The escape route would seemingly be to evade such a bane, but Got Ya! Create Pit is specifically designed to not be able to deal with this bane. While the designers may have cackled gleefully at such a moment, I believe that was a poor decision, as this would have at least given game theory decisions to those playing vulnerable casters. As it is, I am maxing out on attack spells, why evade monsters I can deal with if the only ones I fear cannot be evaded?
The next problem to be addressed is balancing large groups versus those whom play a character solo. A hard task for sure, but there have been murmurs that this set punishes groups of six mercilessly.
Having played another cooperative fantasy card game that forgot to balance for large groups in its third iteration I hope this is not the case! I really haven't went back to that game since then as such a glaring design error really leaves a bad taste. ( Much worse than anything we are speaking about here. There was one scenario in particular that your game would be over with death by turn 2-4 no matter what you did if you played with max characters)
So, to excuse my wall of text, I really do like this game. I have been a vocal proponent locally and have hosted many new players into this game. I hope you take my criticisms as they are intended, constructively.