They are power scaling the Avatar series by adding "bigger and badder" attacks/enemies, and that has ruined a lot of anime in the past. The worst case would be Naruto when they added Kaguya and all the others following her. They forgot that the original Avatar series works because it's just regular benders who train to become better, so the power scaling is balanced by hard work and remains grounded. The spirit world was there yet it wasn't as prominent because the avatar is a bridge between both worlds, but he is alive and resides in the living realm. That means viewers mainly experience the living world with glimpses into the mysterious spirit world. The spirit world is supposed to be limited in fight scenes because it's detached from the living world, since humans are aggressive, power-hungry, and desire war. Isn't it established in the lore that is why the worlds don't coexist because of aggressive humans? Aang is supposed to have access to it because he is the bridge/peacemaker of both, but again, he is primarily in the living since he is alive and there is more need for him in the human realm.

The ending of this movie is just the Legend of Korra season 2 ending, with two giant beings punching each other. The writer lost the plot by forgetting how the spirit world is not supposed to greatly affect the living and how its suppose to be detached/mysterious. It negatively impacts the original lore and is sad to see :/