He is able to kill many armed men facing him at the same time, getting no injury from them. He knows he can easily kill them all. Why?
Usually some explanation is given, like he was born super strong, he has a magic potion, he trained with a master, he is protected by the gods etc.
Here instead we get NO REASON.
Did I miss something?
He is just a kid, and manages to survive the slaughter of all his people and wound a grownup.
But let's chalk that one up to luck.
Later he's a grownup, and he doesn't show any particular skill or strategy.
True, he attacks small groups, but he simply charges upfront like a wolf attacking a deer, even if they are also warriors, but he never gets touched by them.
The final duel is indeed stupid, considering every previous one.
I believe the excuse for the outcome is, other than "the script says so", he gets injured by his little brother, so he is still bleeding fighting his uncle.
I strongly disagree. Good action is great and always believable. I cannot stand bad action.
Die Hard, logical and justifiable action: awesome classic.
Die Hard 4, man vs jet: awful turd.
Never gets touched by them? The only time he attacked a group solo he ended up getting laid out and strung up, covered in his own blood (and they ran at him one at a time to start off). The other battles were either with his group of pillagers, one on one (the "Lacrosse" game) or in the dark, giving him and advantage.
Edit: Don't take this as me defending the movie. I was excited for it and it was a letdown for me. But I do think that the multiple animalistic rituals were supposed to make him beast-like in battle. Who knows, this movie was all over the place lol
He acts like someone that knows he is invincible (he charges head on multiple enemies with zero strategy. He never fails nor thinks he should act differently).
The action never shows or hints at how such a brainless technique would result in a sure series of victories. Realistically, anybody who is not invincible would act more carefully or cunningly, or would at least get injured and in trouble qute often.
THAT is clear and obvious to everyone else that uses their eyes and their brain when watching ANY movie.
In all the millions of conflicts through history, how many times has someone come out unscathed? Quite a few. It happens and isn't all that uncommon. So, after so many battles, an extraordinary warrior like that would be worth making a movie about.
After one. If it happens more times, some reason must be given.
Like I said in the op, in a fiction if you keep winning fights over and over receving no harm, either it is explained why, or it looks questionable or poorly written.
It is NOT a real story, fiction needs to be believable.