[Nibile]

https://pareti.it/alessandro-zeni-ha-liberato-la-placca-piu-dura-del-mondo/
I'd say that it is more a "wall" than a slab, being vertical, but it seems a big hit nonetheless.

[Fiend]

Sounds amazing for something that's definitely not a slab, and from a guy who hasn't done The Meltdown. Hardest wall in the world, good effort.

[Muenchener]

"Platte" in German is usually translated as "slab" in a climbing context, but it extends to things significantly steeper than what we would generally call a "slab" in English. Looks like Italian usage is similar.