Get good. Or ignore the dungeon. Plenty of content in this game. Sheesh modern baby gamers...
There is a difference between challenges that are fun and cathartic to overcome and the ones that leave one exhausted and relieved they don't have to ever do something like that again.
Take D:OS2, for example, with its Mord'Akaim fight in Act 2 and the arena and Adhramallik in Act 4. They all have very nasty tricks up their sleeves that you have to either power through or find a way to prevent them being used in the first place that aren't just ridiculously bloated numbers which reduce every encounter to praying to RNG that you land at least one. Freaking. Attack. You are rewarded for cleverly applying your toolset and thinking outside of the box instead of just metagaming the terribly designed fights to oblivion.
And if D:OS2 is too new of a game to appeal to as an example, how about the direct inspiration for the Pathfinder games - BG2? You have such an insane array of spells (instead of Kingmaker's / WotR's selection of mostly boring stuff and way too many polymorphs that are practically useless, at least in my experience) that you can (and should!) approach difficult fights creatively rather than just slam against them in hopes of bum-rushing the enemies. Why fight an entire colony of illithids with people who have brains they would so enjoy eating when you can summon a single Mordenkainen's Sword and clear the lot of them out? The stuff of blasting does insane damage but gets destroyed after a few hits? Give it to somebody who can backstab with a good multiplier and enjoy the result. Soloing the BG games with a spellcaster is a thing precisely because it allows for some really cool tricks to be pulled off.
Many of them are the relics of the 2e's era of completely bonkers balance of certain magic, but having bonkers magic is far better than having arcane spellcasters who deflate immensely in usefulness past the first half of the game when everything either has too much health or too high saving throws, and you don't have nearly as many nice high-level spells as the older D&D adaptations offered. Hell, an alchemist ends up being a better magic damage dealer than a sorcerer does, since you can just spam a particularly difficult enemy down with force bombs in a pinch. It is also a really questionable decision to introduce way too many enemies who have different types of DR/immunities and not give you any ability to create/enchant weapons (the random gifts from craftsmen don't count) so that you can equip people tailored to a specific weapon type with something actually useful against the more dangerous enemies. What's the point of having most of the weapon types from the rulebook if you don't find any worthwhile versions of about 2/3 of them in the entire game? You can't even reliably buy the at least +3 ones for most of them. Good luck using a crossbow or a - gods have mercy on your soul - sling staff when their unique/magic versions are mostly crap and quivers don't work with them.
Being designed like ass does not an interesting challenge make. It just highlights how the developers have no clue how to design something actually appealing to think about.
Honestly speaking, when playing unfair, I didn't even bother with the spells that require hitting. They practically never hit. In the case of WotR in the second act I practically stopped using any CCs, I decided that it makes no sense if you do not build a character specifically for what is possible and so only at the end of the act, and only because of a single mythic feat that clearly does not work as it should. Spells that always hit but deal less damage on a successful save are probably the only sensible way to deal damage while playing caster. Most of the time, magic is used to buff or summon skeletons (other summons are weak and not worth using).
