Ok ill save you the time , I was in the top guild in the game with the best gear , I put all of my points into dexterity and was fully buffed with food , a +6 bow and full light armour. I have a mouse macro that allows me to release the shot just as it goes red to increase DPS however you can only inflict 55 damage per headshot on a lovl 100 player in full plate , these guys have about 1200 health so do the maths. They can simply walk off with the shield raised and block all further hits whilst they heal. This game is not built for archery the developers hate it.

Videos do not lie this is your standard siege of a guild keep that happens every day and as you see the whole shield wall is wearing plate you may as well throw grass at them

https://www.youtube.com/watch?v=4utZ6Hm5aV4