Gainsaying is an old term for rebellion. I don't dispute the Korah rebellion. Within the tribe of Levi God had appointed different divisions; only Aaron's family was able to go into the Holies of Holy. Korah was from the tribe of Levi but was assigned to move and carry the tabernacle (Number 3 and 4). He and his family of the Levite tribe wanted the same privileges and duties that had been assigned to Aaron's family. This was against what God had ordered. Korah's rebellion was not against Moses but against what God had specifically stated and appointed.
Uhm, yeah.
Num 16:3
And they gathered themselves together against Moses and against Aaron, and said unto them, Ye take too much upon you, seeing all the congregation are holy, every one of them, and the LORD is among them: wherefore then lift ye up yourselves above the congregation of the LORD?...28 And Moses said, Hereby ye shall know that the LORD hath sent me to do all these works; ...