I think bonus focus drop rate should increase based on grade score and/or activity difficulty, since otherwise it doesn't feel worth the second run and so on if it's not guaranteed (especially in PvE) This way this feels more on par with how drop rates for Nightfall weapons got increased based on champion rank and difficulty as well, and gives incentive to go for high grades even at higher levels. Additionally, bonus focus gear should drop multiple times for longer activities, similarly as to how base rewards are higher in those cases.