We'll add most of the judgment when the rest of the sheet is in.

But we're a bit skeptical about the idea of the Sith banishing someone for weakness... They're not that unified. Someone will always see fit to instead use him for some scheme or other, ending in death. Weakness is despised to such a degree that its not permitted to survive. The only way to leave the Sith Order is to willingly leave of your own accord, and thats not generally very easy once they know about you. Once you are in their records, you would have to leave the empire’s reach to escape. 

If he was so weak as to not handle the training at the academy, someone, be it an instructor (or more likely another student) would have released him from that problem through killing him. Sith ain’t so nice as to Banish. Especially not during wartime.

By the way, how old is he?