My main problem with LoK is the Avatar state, to be honest. In Last Airbender, the Avatar state was a last resort, almost undefeatable power, while in Korra it's just a small power boost. That said, the characters and the antagonists are amazing, and I love LoK to bits.
I guess I hadn’t thought about it before,
personally i think it has more to do with the differences between Aang and Korra.
Aang is a pacifist, he is shown a lot as not wanting to really use extra force when he doesn’t have to. So while I could be wrong here I think it comes down to that Aang just never really uses his bending for fighting when he doesn’t have too. On top of that, his early experiences in the Avatar state weren’t really good ones?
1. He froze himself for a 100 years
2. He went into it after finding out about the destruction of his people
3. That general tried manipulating him into it by messing with Katara
4. After going through unlocking all his chakras, when he finally does get them all he almost gets killed
I think the reason it feels like the Avatar state was used as a last resort a lot more in airbender is because for Aang that was his literal, last resort.
Even in Lok, his fight with Yakone, he doesn’t use the Avatar state to attack him, doesn’t use it until he takes away his bending.
Now Korra, I’m pretty sure came out the womb ready to fight, by the time she arrives in republic city she has had years and years of training and was already this power house of a bender and hadn’t even learned to airbend or being able to tap into the avatar state.
In Korra’s first scene of book 2, she uses the Avatar state to boost her speed so she can beat the the kids in a race and Tenzin gets upset about it.
So I think it makes sense that Korra would figure out a way to integrate the Avatar state into her bending to give her a boost when she needs it.
I guess for me I think it comes down to that Korra is a lot more liberal with her use of the Avatar state where Aang was more reserved and only used it when necessary