I have no idea how they could think that this is fun.
Because it is. Apparently you're doing something wrong. Yesterday I defeated the hag without taking a single hit with my bad armed team. (no cheesing, no barrels, no exploits). Combat is super satisfying.
It is really predictable that this "you're doing something wrong" answer always comes.
I would accept this if this was about my job, where I had to work and would get payed for what I am doing.
But a game? Sorry. I am playing games to relax and have fun.
And for an RPG, there should be more than one spell that works, and I should have a decent chance to win every battle with every party. Otherwise I am not interested.
And you mentioned Guiding Bolt. I am not aware that this spell can hit at all. Even when it says there is an 80% chance to hit. it basically misses all the time.
I just for fun startet to reload until it hits. And it takes three to four reloads until a spell with 80% to hit chance hits, and about 5 to 6 for one with a 50% hit chance. In my book that would be more like 30% or 20% hit chance. But hey, who cares about the numbers they show.
It's OK, nobody denies there should be easy/story mode for people like you. If Larian fails to make combats enjoyable (though I have different gripes with the current state of the combat mechanics), I will play on that difficulty as well.
The percentages are definitely buggy, but that will definitely get fixed. I think in the case you mention the problem might be that you have a disadvantage, but the game does not show that (and take into account when computing percentages).