Resized img. Yes your friend has to have leaks if he cant get at least a 3bb winrate which should be easy without table selection.
The thing you have to consider is that if his going for SNE then he has to play like 12k hands a day or almost 9 hours for 365 days in a row. Grinding this kind of volume is going to get you off your A game for sure and you will be playing your B game most of the time.
Add the times your hungover or sick and are forced to play your C game is another reason for lower winrate.
Also to get max hands per hour you can't be table selecting that much. I often don't get more then 16-20 good tables going off hours and im fine with that, but if your going for SNE you have to be at 24 at all times.
Personally i don't think its worth going for SNE unless you play at least nl200 and mixing in some higher stakes as well since they changed the rake system to contributed.