Your posts indicate expectations this game does not sustain by its approach (I'm not speaking of good or bad here) and some kind of unwillingness to accept and use what it offers, expressed by words like 'shitty fight', 'fucking ranged attacks', 'rewards are shit' and 'every single fucking time'. Expectations like special rewards for doing something, crushing enemies on the first round(s) (which is, unfortunately, possible in almost every fight!), always being superior (i. a. quantitative), enemies having low resistance (so CC is always succesfull), low health and low damage values - less than you or equal - (which, unfortunately, is often the case), the game telling you explicitly that there is a boss fight in the blood cave, not having to reload sometimes or level up if a fight was too hard.
Some arguments have already been made, but to response to all your points:
The gory bull gets to go right after being summoned and deals 59% of the max health of my fighter in two attacks in the first round.
Initiative allows you to go first. Control the bull. Don't expect to be succesfull on your first attempt. But your amount of APs should allow you to have several attempts.
So first round the mage is dead. She was also the healer.
It's always a bad idea to rely on one single healing option, especially when having three or four party members that receive damage.
summons more creatures than you have members in your party
As I already said: Why not summoning, too? It's a good idea to spend one point in Geo to be able to summon a spider, or Witchcraft for sceletons if you need support. 3 oder 4 members: up to 6 or 8 party members! + Charmed enemies! So 10 or 12 is theoretically possible. That's just one option.
ridiculous health and damage
Damage can be hard: so control enemies and kill the strongest first. And speaking of health: 388 damage is more than 25% of his health (or did I get you wrong?). And one fourth with two arrows for a 'boss' enemy is quite much! And he's a source mage, not a philosopher
Blitz Bolt stuns him and my warrior. He is stunned for one round. My warrior for two. But that is normal because EVERY SINGLE ENEMY after level 10 or so is affected by conditions one turn less than the spell description says.
If Blitz Bolt stuns both the mage and your warrior something went wrong.
The description might be wrong. Enemies get stronger. But so YOU do. It's possible to end statuses earlier if you have high bodybuilding and willpower. And there should be a talent.
You know what would have been creative? A none combat solution like Mass Effect, one of those AAA titles you talked about above, managed to do. But that game was clearly written by marketing research.
And there ARE ways to avoid some fights, as Raze said. Not for this fight. Can be extended for roleplay purposes, I agree. At this point the game wants you to fight, or not to fight. You don't have to fight him, do you? And if you have to fight, because a quest wants you to fight, so fight the fight as the quest says.
This is a single guy in a cave, not a giant skeleton with a burning skull that everyone told you is a tyrant. Why would I assume there is combat soon?? Try to see it from a new players point of view. You talk to someone and suddenly completely out of the blue you're in a fight you can not win.
As Raze said: there are tons of dead bodies, and blood everywhere. So...?
I can't agree with most of your points, although I don't think that combats are always designed well or the balancing cannot be better.
I remember Witcher 3 for not being a good game for its challenging fights, for example. The combat system allows you to fight enemies within a certain level frame (your level + a few levels above) easily, and sets artificial limits, so enemies you can fight (being close to your level) are generally easy if you got used to the mechanics. And Skyrim? I can't compare it for its broken balancing. Very easy on low difficulty, on higher difficulties absolutely weird relation of health and damage between you and your enemies if you level up (by alchemy, lockpicking or what else). Its difficulty comes from artificiality. - But that's not what I wanted to talk about.
Divinity Original Sin EE is more too easy than to difficult (even on highest difficulty), if we take 'difficulty' as the difference between the worst possible builds and player skills that are successful on a difficulty level - and the possible best (the greater the difference the easier the game). And some summons out of nowhere (which I don't like very much either) and some higher enemy HPs is neither impossible (or very difficult) to fight nor very artificial.
Your conclusion (done with this game) is quite hard, and in some points it does not seem to be fair. That's all I wanted to say.