Looking at the (newly) revised Cypher System Rulebook, much of the ambiguity and apparent contradiction has been fixed.
Some definitions (p 207):
- Inability: The opposite of trained — you’re hindered whenever you attempt a task that you have an inability in. If you also become trained in the task, the training and the inability cancel each other out and you become practiced
- Practiced: The normal, unmodified ability to use a skill — not trained, specialized, or an inability. Your type determines what weapon skills you’re practiced in; if you aren’t practiced with a type of weapon, you have an inability in it.
- Trained: Having a reasonable amount of skill in a task. Being trained eases the task. For example, if you are trained in climbing, all climbing tasks for you are eased. If you become very skilled at that task, you become specialized instead of trained. You do not need to be trained to attempt a task.
- Specialized: Having an exceptional amount of skill in a task. Being specialized eases the task by two steps. So, if you are specialized in climbing, all your climbing tasks are eased by two steps.
With that out of the way, let's look specifically at Weapons.
From p 203:
Not all characters are familiar with all weapons. Warriors know their way around most types, but Explorers prefer light or medium weapons, and Adepts and Speakers usually stick to light weapons. If you wield a weapon that you have no experience with, an attack with that weapon is hindered. Having experience with a weapon is called being practiced with the weapon.
So, not being practiced with a weapon class is effectively the same as having an inability in that class. (The description for Adepts actually spells this out. On page 25: "You have an inability with medium weapons and heavy weapons; your attacks with medium and heavy weapons are hindered."
As for the "extra" hinderance for being un-practiced with heavy weapons; I simply don't find that in the revised CSR. They fixed the glitch!