Archery in this game kind of sucks.

[Celjabba]

Originally Posted by DanHoward

Keep in mind that part of the balance is that archers can position themselves so that there is minimal risk of them getting hurt.

In the OP case, unless the outpost was in the middle of a plain, there are good odds that the archer could have found a somewhat hard to reach position (on a roof, on top of a boulder, ...)
And of course, behind the other players.

If they attacked a well situated outpost with no weak spot, crewed with well-armored ennemies in such number that they can overcrowd the other players and get to the archer(s)... well, attacking was probably a mistake.