I agree 100% with you. Like you and quite a few others, I noticed the precise same issues pertaining to Orbx YBBN and Brisbane cityscape.
From my experience (and I’ll stay relevant to airport scenery in Aus) YSSY from Fly Tampa is a way superior scenery package in both looks and optimisations in comparison to Orbx YBBN. The resolution is Orbx need to rework YBBN and optimise the textures of the entire airport (just to begin with). That would definitely improve frames/smoothness/looks by a large margin. When a developer insists that consumers need to lower their settings to accommodate their scenery…in my experience, that indicates poorly developed scenery and I’ve been flight simming since the early 90’s and have pretty much seen it all.
I still fly in/out of YBBN from time to time, but had to uninstall Bris cityscape as it was further exacerbating my frames/smoothness into single digits/stuttering.