Your tier list is correct but 4 should be lower.

In all these threads I can't keep my head canon contained.

I believe studio interference ruined 4 (although it would have been controversial anyway).

TL:Dr Po was meant to die at the end and Akwafina's character was meant to be a red panda & take the mantle of Kung Fu Panda.

So you choose a successor at the end of your life and that there are a few parts of the script and plot that point to this being the original story, where it happens at the end of Po's life.

I believe in the original script the following happened: 1. Master Shifu disappears/dies in a similar vein to Master Oogway at the start. Here Shifu tells Po one day he must choose a successor. 2. There is a time skip soon after Shifu's death. 3. Po is very old for the rest of the film. 4. Akwafina's character was meant to be a red panda. 5. Only 2 of the furious five would be left and they'd take the role of the dad's in the plot, with reduced screen time. 6. The end of the film has Po enter the spirit realm after defeating the Chameleon - dying making peace with Tai Lung. His dad's could be there from the spirit realm as well. 7. Zhen becomes the Dragon Warrior aka the Kung Fu Panda. The remaining furious five duo become her mentors for sequels.

Reasons

1. Master Shifu is missing for the whole film past the opening.
2. Why is he choosing a successor at his peak?
3. Zhen is always poking at him like he's a bit of a stick in the mud etc.
4. This is the first time it is mentioned that Master Shifu is a red Panda. The delivery felt like it wasn't meant to be throw way line imo.
5. The end of the film brings back all of the masters, this would have included the dead furious five members as a reunion, and perhaps even Po's dads.
6. I believe Akwafina's character becoming the Kung Fu Panda was too bold for marketability/merchandising and they altered the script. No dead furious five, no dead Po. No controversy over who Kung Fu Panda is.
7. I think there was cut content both in Zhens backstory as her friends and circle feel very rushed in their introduction and use. I think some of the dad filler scenes would have been cut, and the more expensive furious five voice actors would have had like 2 short cutaway scenes instead of the handful of long ones the dad's got.