Let's talk Erlendur, and why his character was absolutely ruined because Torvi just happens to be creator's daughter.
Let's start off with Erlendur treating Torvi badly - it doesn't make sense. Why? Because Erlendur seems to see her as an ally first, and only then a wife. That's the way he introduces her to Kalf: by saying first, that they have another ally. And this ally just happens to be his wife.
Knowing how adored Ragnar is by all - Erlendur should value every single ally that he has. He won't have much, because most people in Scandinavia would not support the idea of wiping out Ragnar's bloodline. And the most adequate behaviour in such situation would be treating your ally with respect, so they don't betray you and your cause. And Erlendur knows it - he respects Kalf, and it really is visible.
Besides, this behaviour is not justified. Erlendur's hatred towards Ragnar, his friends and family — yes. He has good reasons to want revenge. But being an asshole towards his wife isn't. Horik, to whom Erlendur obviously looked up to, didn't seem to treat Gunnhild in this way. Following the rule of film: if we haven't seen it, it didn't happen. Erlendur didn't see this behaviour to think of it as normal. He probably would've taken an example from his father because Erlendur certainly adopts the same political views as Horik.
So, I'm jumping to a conclusion that Erlendur is such a douchebag because the audience needs to feel sorry for Torvi, who is basically Y/N in Wattpad fic. Everyone seems to treat her badly, she's so unfortunate etc. etc.
Another minor detail: Erlendur is absolutely demonised for cheating on Torvi, manipulating her, and hurting her by ripping the Björn's gift out of her hands. But Ragnar isn't any better. He slapped Aslaug, killed Yidu in front of his sons, cheated on Lagertha...and yet somehow he's forgiven for that, while Erlendur isn't. But it's just my personal opinion.
Lastly, his death. It was unrealistic for a number of reasons. First, Torvi would not be able to take this shot, and actually kill.
Firstly, because she simply doesn't have the guts to do it. She fainted when her previous husband, Yarl Borg was being executed; she later has flashbacks after an unfortunate attack on Paris.
Secondly, Erlendur was kind of right. Torvi wouldn't be able to fire the crossbow properly. She never had any training. So despite crossbow being easier to use than bow, it required practice to hit a target - to aim, to find the best spot. These skills should be trained in a field, and mastered in a battle. Torvi had neither. And yet she manages to shoot Erlendur right in the heart from quite a long distance.
Assuming her intention was to kill, she'd have to aim for fatal body areas. Such as a heart. She didn't have much time though. Once again, this skill can only be mastered in a battle.
This shot was impossible.
It's purpose was to show how cool and girlboss Torvi is, but it's stupid.
That's all I have to say.
