Welcome back Inspectre! I was about to hire a party of adventurer to go look for you, but it seems I can call them back now.
Wrath of the Righteous
I just finished it a few weeks back, but yes, I would have had a lot of trouble even mildly threatening the PCs if I had followed the guidelines. I actually rewrote the entire set of encounters, and about 25% of the campaign, and managed to have actually quite a lot of fun...and put them in difficulty more than a few times!
First important thing, except for one of them, my players (at least this group) are not powergamers, except for one who took more of a support role (with a Honor guard cavalier/Marshal build), so it avoided the worst excesses.
Second, I banned a couple things, especially multiple standard actions, to avoid the nova syndrome.
After that, I mostly focused on building encounters that would be challenging by being non-conventionnal.
When they fought Jerribeth, a mythic Glabrezu masquerading as an elven noble, I had her kidnapp one of the NPCs they grew attached to, Anevia Tirabade, beforehand. So when they reached her and started the fight (Jerribeth attempts to turn them against a rival didn't work), they had to fight both Jerribeth and a dominated Anevia, who was fighting naked but for her weapons. Why? Well, they had to find a way to stop her and neutralize her without arming her despite and extremely low AC (14, I think), while fighting a powerful demon who didn't care who was in the crossfire.
When they fought Xanthir Vang, a Worm-that-walks wizard (and father of one of the PC), I relocated the fight to the cathedral nef, where he had taken the liberty to trap the place with word activated glyphs of warding, resulting in a dynamic battle against him and his cronies, while avoiding the explosive stones.
I reworked most of the encounter along those lines, trying to push them towards creative solutions with more or less success...
I had a lot of fun with Minagho, a Lilitu demon with Rogue levels that the player consistently foil for the first four chapters. So I took the suggestion of having her harass them in the city of Alushynirra, where they try to get an audience with Nocticula, but I took it much further. She planned ambush, stabbing them from the crow, shooting at them from distant rooftops, attempting to poison them, turn the crowd (a crowd of mostly demons!) and the guard against them by spreading rumors and paying off people, and generally remaining incredibly slippery. They had to get a scroll of dimensional anchor to finally corner her, and even then she remained very dangerous.
So I believe it's possible to actually put the PCs in danger in this campaign, but it's probably more work than it is worth.