Learning by pain
Just think about it other way, after failing you want to solve that, and that's what keep you playing.
Would you have replayed the SoH without failing? That's what keep the players, if you know what will come you would have spent less time playing the game. And the time you spend inside the game is the only thing that really matters.
If I had been playing on Ironman I would have been totally pissed and WOULD have probably thrown my phone. It's one thing to encounter a tough puzzle or a tough boss, it's another thing where you either have to DIE multiple times or consult a Wiki to figure out when and how often you'll need to respec your character to survive various environments. It's pretty much impossible to know until after you've failed OR consulted the Wiki. I don't think that should be the case. I think the in-game dialogue should at least give you some warning.
Something that Folcarad might mention, for example: "Beware, should you venture below; there are rumours that monsters dwell there which can paralyze even the bravest adventurer, and even talk of a lower level where flames consume all who enter!"
See? Simple enough. No need to consult the Wiki, no need to go in unprepared. Unless you're not paying attention, you can tell from that bit of dialogue that you're going to want Spirit and Fire resistance built up. Right?