Armour isn't a bad thing. So a quarter of the army was better than the average, protected barbarian then. That's the point. It's an army that can have a considerable amount of quality troops. So it has an edge over all the one-dimensional armies out there. Last but not least most armies perform better in period.The tournament I won was an in period 1000 point doubles comp. There were a total of 8 bases of superior and the maximum 24 bases of armoured out of a total army of over 120 bases. I don't think that 8 bases of superiors makes the army..... And if we are now saying that armoured is also a bad thing then I am not sure what you can actually use.
Take the slave revolt without roman equipment to an open comp and decide if they are still a good army.
So two opponents of the Libyans spent loads of points on things they didn't need. Actually good match-ups then. How a Mongol Conquest managed it to get routed by unproteced MF will be theirs and yours secret, I guess.

Anyway, you are a good player so I'm unsure what that says about the army itself. Unfortunately we lack enough data to really estimate the strenght of the Libyans.
But they are also an army who could field a good amount of superior troops and the army list even allows for the feared air'n'grit structure. I wouldn't rate them as very bad army.