After a further testing it seems the issue is a bit more to the point that the Global debuff is not applied to the B1 battle droid. Most probably due to the fact that it is being revived all the time and does not really have proper protection. Hence it is not properly affected.
Drawing conclusion from that second report:
https://answers.ea.com/t5/Bug-Reports/Superior-Training-Proving-Grounds-ignored-by-revived-Characters/m-p/11397615#M57957
Where The Nute Gunray in the screenshot started with reduced stats, but revived to the current health and protection. Hence the proving grounds seems to Not properly interact with B1 and Nute, And additionally a Summoned Sniper droid.
Update 2: Additional information. Doing 10 battles more proved that it is not being applied to General Grievous neither. If it starts with its AOE on tier X it oneshots entire friendly team of R7. Except KRU maybe. Proving that 80% reduction in offence does not apply to GG.
