Overall difficulty is fine for delves, way too easy for raids minus queen, and way too brutal for keys.
The OP has decent enough ideas. I don’t know why we’re singling out GB trash when bosses, including GB, are far more brutally tuned and the problems…and it isn’t even the bosses but tyrannical and fortified itself.
Get rid of both or move them to +15 and beyond levels (combine them even) and put a movement affix on +4 and a damaging/mechanics affix like bursting at +9. We already have key scaling for bosses and trash. Mythic+ is now fixed.