QA / TA can only proc once, DA can proc up to twice. If a QA / TA proc they preclude a DA from procing. This was first noticed by DD's without TA getting weird returns on WS's. Now we've got so much DA available that it happens pretty often. Those extra hits are still subject to acc cap though, so the more you have the less likely they'll all land.
Anytime your in positive DA then Brutal wins, it's only when Brutal's effective DA rate drops under 5 that other items start to beat it. Honestly the STR earring is rarely the best choice in slot, there is a reason nearly everyone use's brutal.