The punishment is fair in my opinion, if he returns the money that'd be even better. The effect of being imprisoned could already destroy his life aswell since it's gonna be hard for him to build his career. hopefully it somehow scare off any hackers from doing any such criminal activities more specifically those from 1st world countries since they are more likely to get caught seeing a more strict and "real" law enforcement.
If he will not return the money, he will more than likely use those stolen funds after he gets out. Who knows, he already transferred it to a secure place where he will be the only one who can get access to.
The amount of BTC that he gained from this hack would be worth over half a million dollars so this is not such a terrible deal but I still don't think he should do any prison time at all. Nobody forced users to send him their bitcoins and it was Twitters fault that they didn't have adequate security.
So do you think websites offering ponzi scheme or project offering unrealistic gains is not scam also? Because it's only a words and promising, they didn't forcing anyone to send him Bitcoin too. You're wrong then.
Hacking someone twitter accounts is already violations, why the hell someone need to use someone account when you can use your personal account? As you know many peoples is trusting official account, that's why some user send their Bitcoin to them without worried... because they're believing.
Yes, these MLM or ponzi schemes also need to be punished. However, if there will be no individuals or groups that will push thru the case, they can just run away freely. This is why most ponzi schemes can get away because very few individuals can dedicate their resources of running after to these scammers.