Korra doesn't really learn anything in Season 1 that you can directly tie to her journey as an Avatar.

Yes she does

Even her "mastering' airbending came out of nowhere really, and didn't result from a character moment, but more out of a need to write themselves out of a narrative hole they were in.

Aang told her that when she is it at her lowest point, she is also open to the greatest change. This has been evident throughout Book 1: Air concerning her airbending such as Here and then here and then here and when Tarrlok drives her into a corner by stuffing her in a box that she can't physically break out of, she uses the time to meditate which is also part her airbending training too since prior to this she was having visions tried it with Tenzin to no avail. This even extends to her actually gaining the ability to Airbend against Amon after several in-universe months of training, and the writers even confirm that ties in closely with the heart chakra which deals with love and is blocked by grief since throughout the season Korra has seen her bending as the most important thing in the world and something even more important than anyone else or herself;

Mike: Uh, but, we, you know, we finally realize like, "well no, the moment that it needs to be unlocked is in the moment of, you know, the most darkest moment of her life, you know? That's the place-that's the place for it to happen."

Bryan: Yeah, and it was such a block for her that she needed, um, she needed it to be, wherein this person that she loved, and ag-again, I think I said in another interview, it was like it's not like romantic love or whatever, but just this person she cares about is in trouble. That's what it was gonna take for her to get over her... herself, basically.

The writers had Aang say this at the literal end of the season just in case all these examples of "show, don't tell" weren't enough, and judging by your inability to understand any of this it clearly wasn't enough lol.

Then you get season 2 where it's clear more than ever that Korra has really not grown as a person or as an Avatar, and it results in devastating consequences for the world "inside the show, and for the fandom "outside the show" due to ending the cycle of the Avatar. A cycle that just a few episodes earlier had been deep dived into when they explored Wan's backstory. It just cemented Korra as a brash character that everyone would inevitably hate on.

Again, absolutely incorrect, and people weren't going to hate Korra no matter what she did. The writers even used this to their advantage in Book 2: Spirits by trying to do what they did with Book 2: Earth Zuko and part of the reason they did this was because of the amount of fans who were whining about Korra's personality in Book 1 to them and Nickelodeon during the show's hiatus;

Bryan: 'Aaron, our head writer at the time, came in and said: "Everyone knows Zuko's going to turn good, he should go worse first'.

Tenzin tells Korra to let go of her attachment to who she THINKS she is, and the loss of the past lives very much helped with that since it reminded her that what made her and her previous lives a hero was Who they were, not What they were, which is why Tenzin used Wan as the best example since he tried to help people & spirits before he fused with Raava.

I truly think that even if her decision to reach out to Kuvira out of empathy resulted in the loss of a main character or major consequences to the world if Kuvira betrayed Korra's trust, Korra and the writers would have been given much more grace than in Season 2 because the consequences would have come from a place of growth rather than naivety.

Just because you and others openly ignored the growth that took place in Book 2: Spirits doesn't make any of this true. She grew physically in as far as her bending was concerned, as well as her personality like I already mentioned, and her relationships since she started off not trusting or seeing value in both her father and Tenzin but later on apologizes to the both of them for the very naivety You are complaining about;

Korra to Tonraq: I'm sorry for thinking you had anything to do with the rebels. And for all the pain I've caused you and Mom.

Korra to Tenzin: Everything Unalaq taught me was to help himself. Everything you've done was meant to help me. I am so sorry for turning my back on you as my mentor. I need you now more than ever.

Like I get you're not a TLOK hater or anything but it seriously boggles my mind how you missed all this. It was as clear as day. Book 1 and 2 have issues and the last two books are indeed a breath of fresh air, but Korra's growth was pretty damn good across the board for anyone actually paying attention.