Maybe Cho + Stoneplate isn't intended.

Gargoyle's Stoneplate reduces damage by 60%, specifically to prevent champions with health-scaling damage from doubling their damage. There aren't many champions who do so, but Cho'gath is one of them.

And unfortunately, they didn't bother doing the work to code Stoneplate's damage reduction as an exception to the usual inability to reduce true damage.

But the very fact Stoneplate reduces damage dealt at all is the proof that they did not want health-scaling damage abilities to 1-shot enemies.