I don't think the frequency of Hunters was to do with them being easy to kill with a pistol shot to the orange flesh (the front being easiest like scarab said); and it's not like you'd necessarily be carrying a pistol anyway. I'd say it's just to do with them adding variety and looking great.

: In Silent Cartographer, three pairs are placed indoors, in very
: confined spaces.

Actually only two pairs indoors (security substation and main facility); the other two pairs are outside.