At this point, Attribute Level mostly affects an adversary's starting Hate score and provides additional Endurance loss when activating Heavy Blow (p.143). It can also serve as a barometer for LMs when building encounters.
If I remember correctly, in TOR1e, Attribute Level was used a lot in special abilities (base and bonus damage and such, like with a Dragon's Fire Breath).
As we get more adversaries in upcoming material, I suspect that Attribute Level will interact in a similar fashion with new Fell Abilities (something I have already begun to employ in my own custom stuff).
Thank you. This is helpful!