With the warden pickaxe requiring a netherite pickaxe to be upgraded it feels off that it cannot mine the ore.

Can confirm the warden pickaxe does in fact not drop any raw ore when used in breaking allthemoddium ore.
Presumably the pickaxe's mining level either is not correctly set as netherite (or higher) by the mod author or the allthemoddium mod only allows the netherite mining level and not any "higher" levels except allthemoddium itself of course to be used.