You mentioned the priests in Malachi were like the priests of Today. Unfaithful wicked Shepherds.
Yes the priests were unfaithful to God, but so was King David and King Solomon.
But God still used them. Solomon slept with hundreds of women and burned incense to demons, yet God gave him more wisdom than any man. King David was the most famous King of Israel, a priest, a prophet, a king, and a writer of Sacred Scripture, a man after God's own heart, yet he shed much blood, and had one of his right hand noble men murdered so that he could get away with impregnating his wife. A great sinner yet God worked through him. So anyone who behaves scandalously doesnt necessarily mean they dont speak the truth or are not called instruments in God's hands.