An alternative is not give veto to the council, let the contributor be promoted, and watch their behavior. If the new core dev is quickly identified as toxic, there is the conduct workgroup to take actions against the core dev. The conduct workgroup might even provide evidences of misbehavior which can be analyzed by everyone, rather than using a veto without explaining anything.
Maybe a contributor misbehaved 5 years and has a long history with one member of the council, but changed their behavior. There is a risk of abusing the veto power.
No special power, no risk 