Unfortunately anon, you are not wrong.
While CPS will always investigate a claim or tip, there can be a very high barrier to them actually removing minors from a household. And a CPS visit that doesn’t result in removal from the household can result in greater abuse. That is the reason its necessary to use your best judgement for if you should call CPS for your friend.
My personal recommendation is to call CPS if there are clear signs of physical or medical abuse. If your friend has visible bruises/injuries, is malnourished, or their parent is refusing medical care for a physical illness or injury. Unfortunately for all of us CPS does not often intervene in cases of emotional abuse.
The best time to call 911 is in the case of an active incident. Such as if your friend texts you ‘he’s screaming/throwing things things again’.
Because the authorities don’t often intervene in cases of emotional abuse, the best thing that you can do in those cases is bring the abuse to the attention of adults that you personally trust. Non-abusive parents or relatives are the best here.