Improved/Superior critical vs Adamantine Armor DnD 5e

Without adamantine armor a critical hit is an auto hit regardless of AC. Though sage advice ruled that a “Improved/Superior critical” attack auto hits when it lands on 18 or 19 BECAUSE it’s a critical hit unlike in PHB where the nat 20 auto hit is an entirely different wording

So my question is would a champion rolling an 18 or 19 on an attack roll auto hit against adamantine armor? I’m assuming it doesn’t since it would take away it’s critical hit status which is the only reason it auto hits.