Potions are widely available. Just visit a temple.
But those potions don't really do all that much. Most of the stuff you can buy at temples are healing potions, of which only the extra healing ones can keep pace with enemy damage in any meaningful way. And while many buffing potions can be useful (like Giant Strength or Invisibility), those are sold in a far lesser frequency, and can get somewhat costly if used with any frequency.
but you can also purchase potions of magic shielding and magic blocking.
Which do jack shit against most of the high level mages. Blocking 5th level spells and below for a couple rounds is none too impressive against a lich slinging tons of high level shenanigans and having 50% resistance to magical damage for a few rounds isn't too helpful either. The ones that grant 50% magic resistance might have been nice, but they're as scarce as Arrows of Dispelling in BG2...I guess the devs actually realized how good they were.
Use one of the many items, spells or class abilities that prevent a character from being charmed
And doing so is contingent on having these abilities/items and in multiples. Which would likely require foreknowledge or experience to know which items work to disrupt mind-flayer psionics (e.g. a Helm of Charm Protection will, like the goggles, do nothing whereas Chaotic Commands is effective, if brief).
buff him or her if needed and whack those enemies with one of the multiple +3 or higher weapons?
Umber Hulks will likely maul a solitary Fighter that doesn't happen to be some powerful Dual/Multi-class.
That encounter looks much harder on paper than it would ever be in an unmodded Baldur's Gate.
So do most "challenging" things in RPGs. Hell, single-player games in general.
Except gold has barely any value once you've paid the 25k you need for both the mage licence and the ship in BG2.
Not really. Extra healing potions are ~170 gold each, good buffing consumables range from 400-1000, equipment or forging might run you 3000-10000, magical ammunition/recharging will be a constant drain on your wallet and that's with some 21 Charisma munchkin imported from BG1 using the Blade of Roses or Nymph Cloak. Most players will likely feel some constraints on their resources. More than can be said of many RPGs, especially so called "challenging" ones.
I don't know how much PnP DnD have you played, but you normally don't do a whole dungeon in a single afternoon, especially if it's not well under your level (encounters of the appropriate level for your party should take away ~25% of your daily resources). You also have a bunch of ways of resting in a dungeon.
PnP and PC D&D are wholly different animals. You can't save/reload if an encounter goes bad in PnP and then just rest and prepare the correct response. And if you try and rest-scum, any competent DM will have you ambushed by wandering monsters. A cRPG has a lot more difficulty adapting in the way a human DM can; you kind of have to "play around" this if you want to enjoy the games.
You got me there brother...I'm not familiar with that one. Not before my time...just one I happened to miss, I suppose.
But come on....throw me some cheese, brother.
My general point is not that BG2 is some great milestone of difficulty. It's not. But it's clearly a lot more hardcore than some arbitrarily large percentage of RPGs and challenging enough to promote some modicum of thoughtful play. Making an argument that it is bereft of challenge because all you need to do is "just read the descriptions and use the items, bro" seems silly because practically no RPG could be considered anything but a braindead endeavor when you assess difficulty in such a way. Few RPGs require you to do more than invest a bit of time in grokking the systems and then implementing them in the (often static) content. It's just not a terribly difficult genre when you look at them from a perspective of perfect interpretation of the rulesets and have multiple "shots" at any given piece of content.