Moreover, if steemflagrewards take rewards from the pool for flagging, the rewards will not stay in the pool anyway.

True, and it's not perfect but who would you rather advocate? The scammer who rubs their hands with glee at the thought of easy money or pre-vetted Steemians who give a shit and cares about their platform?

The latter group will receive the rewards, but these are people who write content of substance, not crap.