From my experience, there are three levels of damage:
- that "whoosh" sound, arrow did no/just a few points of damage, no stagger.
- the normal "ouch, arrow hit me," brief stun
- the BAM, I ran into that arrow/survived a headshot, that really hurt, tons of damage, long exaggerated stagger.
I've worn plate armour a lot. Only the MW Bodkin headshots that I survived did the "long stagger" Silveredge is speaking of.
It's all damage-based right? Harder hits (speed bonuses, headshots) seem to stagger more.
If so, I don't see what the issue is. Big hits from 2H weapons can knock my character back a bit, hearty polearm stabs do a meaty stun.