Yes, it's strictly sideboard. And when I do decide to board it in, I prefer to play two copies.
A five-color good stuff deck needs time to function. They usually have some enablers, some stalling, and some win conditions, and need to deploy these in the right order. So disruption works. You need to be vary if they have a Raise-dead effect, but mostly they won't play their win condition until the late game, and it's very possible to mill it away and leave them unable to win. Plus, nobody expects that. And they usually don't have a fast clock, since their early game is defensive, so you can afford to play the do-nothing card instead of a late drop which won't do anything anyway as their late game is stronger.
Another good home for
Navigator's Ruin is the Vampires mirror, where you usually have some 1/1 lifelink tokens you want to attack with anyway, and the life totals can stay near twenty for a long time.
And it might be I'm playing that just because the format is so boring ...