I just wanted to mention I did this with 3 level 1 pets and saw that they got a total of 28 xp, so I figure I shouldn't bother with 2 pet strategies on this quest. Agree? Remember for the achievements you need all level 25 pets.
One shot it with this, but my level pet didn't swap in. Ikky swapped in after my starlette was stunned, and finished the rest of the battle. The Wind Up on Chum crit (P/S starlette) for about 1.5k, so I'm not sure if Ikky would have finished the rest if that didn't happen.
Changed the line from change to Ikky when stunned to just standby. Haven't had the chance to try it yet, not sure how it'll work out.
Let me know how this works for you guys, for me this allowed me to get a controlled swap on the leveling pet to eat the stun every time. Further the same amount of damage is taken by Iron Starlette as in the original strat because he now attacks first on the Opening and Final Pets. This also makes it much easier for Iron Starlette to decimate final pet on the field due to already having wind up charged, so he comes in first Supercharges and kills the final pet even if he dies once due to machine passive.
When Chum uses the stun is random. I was trying to come up with my own strategy before I found yours, and it was the bane of my existance. So unless there's some kind of RNG manipulation I don't know about, there's no way to guarantee your leveling pet eats the stun.