The worst thing is that D didn't even really kill Blue Keeper, he got screwed out of the fight himself, but he's taken all the heat from the LTC.
I don''t think Blue wouldw ant her wasting away focusing on revenge on this one guy. She should be killing Peltrola.
Also I think we may be approaching a part of the series where D will begin to fight with rangers on (somewhat) even terms? I can only imagine the gift from Giga Invader will do something like that. This Was Foreshadowed.
(Plus it's D's entire goal, fighting with the keepers directly.)
As an aside, we also never actually had it explained what happened to the Red Keeper that he stabbed through the heart. Like, I guess the implication is either that guy was a clone, our current Red Keeper with the neo rangers is also a clone, or they were both clones. Maybe there's an 'Original' Sosei out there we've never even met.