First of all we have to accept that D4 is mainly designed to be a casual game and grinding out hours and hours without getting valuable Results is not fun.
Also most builds require certain mythics and uniques to work properly, especially in higher Tiers- decreasing droprate = decreasing fun
Rare ancestral item droprate will only lead to even more frustration with tempering
Looking for perfect rolled items should be fun not waste of lifetime.
Drastically decreasing droprates for all those said items will only lead to scaring away players and increasing chinese botfarmed item trading.
So for tormented world tiers increase the droprate of all those items in general.
And for target farming increase rates like Uber bosses in T1 drop 3 guaranteed unique items, rest is ancestral, T2 drops 4 uniques, T3 drops 5 and T4 drops 6 uniques.