#ik things are a bit diff in the shows sometimes but i stand by this (this is primarily movie centric)

[westwindy1]

Neither Hiccup nor Astrid would make a good Chief. Hiccup is an inventor and a wanderer; he's innovative but he's not particularly considerate when he's making decisions. He doesn't think about other people, he just jumps right into things and the other Vikings just have to tough it out and suffer the consequences.

Hiccup leading the Vikings away from Berk was stupid, he was displacing hundreds of Vikings and putting them at a tactical disadvantage, so was trying to befriend Drago in 2 and in HTTYD 1, he definitley was not thinking at all with the whole bola thing. It's really obviously implied that his inventing and trying to shoot down dragons caused problems before and his repeated efforts to the same end pre canon really shows a lack of thought and consideration for others.

Astrid is an amazing warrior; she's razor focused and determined and excels under whatever set of rules she's made to operate within, but being a good warrior does not mean having good leadership skills, expecially when part of being a good warrior means being good at deferring to other people. She leaves it to Hiccup to make the eccentric decisions, like in the first movie with the dragons.

When she takes initiative, things don't usually end up well, like when she was smack talking to Drago. She's not an out-of-the-box thinker; There's just not much sense to it.

Astrid also defers to Hiccup too much, even in the third movie where the decisions he makes are heavily led by her words; she never outright tells him to do something, just implies and implies and waits for him to get it, and the ends she's working towards aren't even for the best of the village; they are, in part, self motivated.

Neither of them listens to other people; Hiccup listens to himself and what he thinks is right even when it's not and Astrid listens to the lead. Everyone else just has to follow along.

Hiccup CAN'T lead.

Astrid can't, either.

A good Chief would consider the voices of the people, they wouldn't be trying to push people into working for their own personal motivations. It should be the opposite; they would instead take the improvement of the quality of life for everyone and their physical and mental health as their first priority.

A good Chief would WANT to do that, which is also why I don't think either Hiccup or Astrid would be great at it.