The reason the Warrior and Cinderhulk enchants are good is that every champion of their class benefits from everything they give. Bruisers like AD, armor pen and CDR. Tanks love having tons of HP and they love a Sunfire Cape passive. Magus may be subpar but every AP jungler benefits from AP and CDR. A Sheen-based Magus on the other hand would benefit AP junglers massively differently based on their kits. Some junglers would love having it and it would be basically worthless on others - the enchants aren't meant to be that specialised.
80 AP is more than enough to make clears faster. 20% CDR does it too for people who are happy to spam abilities on a camp. No, the item doesn't give anything jungle-specific like the Cinderhulk aura but it doesn't need to, it's a GOOD thing that Magus gives you stats that are also useful outside of the jungle while still helping your clear.
The only change that Magus needs is added mana regen. Put a Fairie Charm in the build path, reduce the combine cost accordingly, reduce the CDR to 10% and give it 50% mana regen. Boom, Magus is pretty much perfect. The way to make AP junglers viable is not a Lich Bane Magus. That's just how to make one or two AP junglers viable while putting other ones in an even worse spot.
