Of course, it's necessary.
First, collecting the Gate of Truth requires large-scale rituals, so the location needs to be fixed, and mages can't just be chased around indiscriminately;
Second, although there are no hints, they all feel that interfering with the Time Continent this way is already at its limit. If they dare to personally massacre Two-winged Mages, the Void Realm might very well bring disaster upon the Heavenly Kingdom; don't forget that the Void Realm has a temper;
Third, collecting the Flowing Gold River isn't a one-time transaction, they will need to activate the "Flowing Gold Gate" many times in the future. If they ruin their reputation, no mage might be deceived again;
Fourth, Ash is not very willing.
Thus, the three Divine Lords humbled themselves to come to the Time Continent for a charity event, truly sending warmth to the countryside.
