Trundle e doesn't remove rift scuttler defenses

Trundle's E isn't a knock-up or knock-back.

The ability creates terrain at the specified location and any champions at that location will be moved off of the newly created terrain.

While this ability can result in your champion being moved, it isn't actually a displacement or hard-CC. It functions identically to Anivia's Wall in this regard.

This is why it can affect an Olaf during his ultimate and champions who have been Black Shielded by Morgana.

you mean the knocback or just the slow?

Scuttler doesn't lose any defenses because Ice Pillar is just minor displacement and not actual hard cc.