In the Avatar State, you are at your most powerful.
NO NO NO YOU ARE LOOKING AT THIS THROUGH THE WRONG LENS.
The avatar state is brought through oneness with yourself and your previous incarnations, however, in order to achieve such oneness, each avatar has a different personality and different problems that require training in order to reach that state.
First of all, Korra is a teenager activating the avatar state for the first time. Aang was 12 when he activated it for the first time. Korra should have activated the avatar state A LONG TIME AGO, therefore demonstrating that she has severe blockages. She began her training sooner than Aang for more time than Aang is far more skilled than Aang in all of the elements except for air, obviously, but her continuous and consistent avatar training has prepared her for the avatar state well except for one thing: her flaw of lack of spirituality. This reason is also why Aang always appeared in visions and couldn’t appear to her clearly like Roku with Aang. Korra does not need three seasons of pain and suffering because Korra never had to come to terms with pain and suffering like Aang. With Aang, because he is as an airbender he already has innate spirituality, but his flaw was that he had to come to terms with the pain of abandoning his friends and everyone he knew.
So Aang and Korra do not need to go through the same process to reach the avatar state and should not be held to the same standard for how they should reach it.
Also it’s really hard to read when people tag in hashtags :S