The helicoil is actually a spring. Somewhat reducing in diameter as it is turned in and then presses against the outside threads when the turning force is released.

BTW, I've used threaded inserts in teak very successfully. I doubt I could turn them out. King Starboard is soft but IMO it would hold. Haven't used inserts in King Starboard but I think it would work. I have drilled and tapped into King Starboard and it has held fine. In fact drilled and tapped threads have held my radome to an adapter plate I made of one inch King Starboard when I was in Annapolis so it is about 15 years now.

As for galling, I wouldn't expect that in this situation. The only bolts I have seen galled were in very heavy load situations. My chainplate bolts were galled badly due to deformation under stress.