As a casual player (in that I don't really optimize/minmax/strategize/buff/etc) with well over many hundred hours DOS and now BG3 combined, I think the most concerning thing to me is how the difficulty curve plateaus at a certain point. As others have said.
I enjoy normal modes, but the normal mode was not normal. It was too easy and tbh I enjoyed it for my first playthrough. Nothing wrong with Larian basing their modes on a majority audience. The more hardcore subset is almost always the least/last tended to.

But back to what I was saying before -- the difficulty curve.
I think around level 4-5 is when it really starts to flatten out.
Our groups gets more L1 and L2 slots and now L3 is getting into the mix. Martial classes get extra attacks. Action surge only requires Short Rest :o
Alert feat on all characters. I'm sure you guys know how that plays out.
And oh man, the gold/resource/magical item economy in this game. It's a lot for any hard mode.
Hang on to LaeZel's undies, we're still in Act I.

By the end of ACT 1, I say there is no real danger. No real feeling of "Oh god, I need to craft/strategize/optimize gearsets/etc", it's just rest and go.
And the enemies? They don't really have those sort of abilities that scale with the players' newfound ones. There are no devastating abilities. Moments where rolls were just terrible all around and made for a crap encounter regardless of buffs/debuffs? Sure. But is that all we rely on? The enemy needs to scale with the player in not just level, hp, mob density (to me these are just artificial factors and more prone to causing annoyance and unnecessarily prolonged fights by themselves), but in the variety and quality of their abilities that match what's available to the player. Not just whip on a single person 3x in a row and every now and then throw a patch of [insert element here] on the ground. The enemies are simplistic to a point that you start to catch on to the heuristics of the AI. A true iron difficulty should make the player feel as if they must use everything within their power to succeed with degrees of realistic limitations.