But this is where I've heard other opinions (on wattpad) in 3rd-limited. They say the narration changes from scene to scene as the POV character changes. I believe the narrative should be consistent throughout the novel.
That's different. The narration should change as the story progresses, typically the narrator will use longer sentences when explaining details, but shorter ones when the action picks up, but the narrator should speak in the same manner (same accent--or lack of one--same formality, etc.)
I think you can do both, keep a particular speaking style for a 3rd omni narrator while still modifying his speech to fit the situation.
The only time I've changed the narrator's voice in a story is when I've written in 1st person and head hopped to do a chapter with another character, then the narrator was the other character.
Ernest, I think that's usually the assumption, but I was responding to a comment by an author who said they wrote everything in a Texas accent. I agree that it's difficult to write in a foreign (to you) manner, but that's why I said you've got to actively consider what voice you want for your narrator.
The issued is not with omni, but with 3rd-limited.
Switch, in that case, you can modify the narrator's voice, say as he slips into a catatonic state, his psychiatric medication wears off, or his hatred of the MC/bad guy gets to him. 'D