LARGE Octoquad instability

That is VERY good to know! I found a page on ardupilots documents archive that mentions this exact information: Motor Thrust Scaling — Copter documentation

@Eosbandi Thank you for bringing the possibility that T-Motor 80a 6s ESC’s have built in linearization to my attention. I will have to get in touch with T-Motor to see if they have any info regarding this. However after reading this thread:
(AutoTune in 32inch quad result in strange PIDs, crash in next flight - #6 by AngelAlbeniz)
it seems T-Motors official stance is linearization is not built into any of their ESC’s according to dkemxr in the above linked thread.

AngelAlbeniz from the above thread also discuses issues with MOT_THST_EXPO values regarding his T-Motor ESC’s and motors. The difference is AngelAlbeniz is rocking 32" props and what I can only assume are T-Motor U13 motors. What has me apprehensive about moving my MOT_THST_EXPO from my current .74 to .1 is the data that was obtained from AngelAlbeniz measuring the motor thrust expo in a thrust stand and obtaining the correct value to be .4 for his setup, in addition with the testimony from dkemxr that most T-Motor ESC’s do not have built in linearization (although I will have to confirm).

Because I do not have access to a thrust stand I believe the best course of action is to gradually reduce the value of MOT_THST_EXP of my build (18" props U7 V1 motors) by increments of .1 down to either .4 or .5 observing the results as I travel down the values.

On a side note does anyone have a suggestion on a thrust stand that is capable of collecting MOT_THST_EXPO data in a price range under $600? Ardupilot forum links to these 2 testers

and I’m not sure the $100 Turnigy is capable of collecting MOT_THST_EXPO data (correct me if I’m wrong)

Hopefully correcting MOT_THST_EXPO combined with setting up harmonic notch filtering (thank you @xfacta )Will eliminate the strange de-syncing behavior observed in my initial log post and eliminate the aircraft behavior of rocking diagonally during pitch and roll autotuning.
I will post about the results after implementing these changes.
Thank you all for taking the time to impart your knowledge!