hi! in SWDanny's videos on YouTube, I've noticed the same rocket lagging much more with struts than when it was all floppy, I wonder if perhaps the joints "trying harder" to stay together could be contributing to the lag?
I'm saying this because in another game (Scrap Mechanic), the devs recently added a 'Simple Physics' mode, which greatly weakens the joints (more floppy) but also greatly improving the framerate, so I wonder if perhaps a similar situation could be at play here
if that's the case, perhaps making strutted parts be hard-physics-parented could help with performance, and leaving physics joints only for rotors and whatnot
here are the two videos by SWDanny, with timestamps:
laggy but stable: https://youtu.be/5X2xAfZd7GU?t=109
smooth but floppy: https://youtu.be/ryph3269OjU?t=261