Another thing to note: as @de0u pointed out to me when I asked a similar question, GOS/AOSP has toggles to disable each SIM completely. The only waoy to do that on iOS is airplane mode or not unlocking the SIM, but on GOS, you can always keep the SIM off with the toggle.
Having it unlocked isn't a meaningful security risk if the phone itself is secure. If the phone is locked, it doesn't matter if the SIM is unlocked. If placed into another phone, it'll need to be unlocked again.