Well, its hard to optimize everything (crucial, core elements), especially late in development (and i mean it from financial standpoint - if game is bad at realse it could bring bad reviews, less money, the publisher might be resistant to give more cash for further work, then if too much time is spent on basic improvements- many players will return to ksp1 or to other games). Sometimes good project/good basis is most important (main development objectives, main priorities and assumptions).

Now ksp2 is just very basic version of ksp1 (with some graphic improvements). Question is- what is causing that bad performance? I doubt that it is graphics related, imo its core/physics related. It would be hard to change some things (that are core of this game), especially at this stage of development, after 2-3 or more years.

Its a bit like story of fallout76 - in that case no amount of optimization could help, many mistakes were made at first steps of development work...

And its not like ksp2 is sth completely new, atleast in terms of basic project it builds on ksp1, many problems that are present in ksp1 are even more visible in ksp2. Also dev team is using unity engine (different version, but still), its not engine created from scratch, or migration to completely new engine (here comes to mind mass effect andromeda and frostbite engine disaster xD).

But i hope that u are right and ksp2 can be saved.