ORIGINAL: brknprops
Aresti is a simple and straightforward language, and while i think you can survive in basic without being able to read it, the unknowns in the upper classes pretty much require it. As Danny said, trying to fly a sequence off a narrative is very difficult and requires the caller to be focused on the narrative rather than the flight. Using Aresti only requires a quick glimpse, even for complex figures.
I think it is far more important for the caller to know Aresti than the pilot. After all, the pilot isn't looking at the sheet so it doesn't matter to him whether it is words or symbols. To use your example of unknowns, the pilots may try to memorize the sequence prior to flying it and I'm sure that many can memorize it, but all of them depend on the caller to articulate with words what the Aresti symbols say.
I can read the Aresti and by that alone can figure out what to fly. I think I also know how to fly it based on the rules. (Execution is a different story though! LOL) But the first time I had to call for someone I didn't have a clue what to say. I think this communication is a key part that is missing. "What are the words used between the caller and pilot" is something that is available in very few places. So while it is important to know Aresti, it simply cannot fill that gap.
I'm bringing this up again because Dicksnyder was asking about how to tell a pilot what to fly and also because of my own difficulties in calling for someone. In my opinion, this is a critical communication skill and isn't really illustrated anywhere save a few videos.