I for one would not feel comfortable giving my SSN to an international tech giant, and much less Nexon that hasn't really done that much to earn our trust. After all, it's a piece of sensitive information that could be easily used for fraud if a security breach was to happen. It would probably also violate GDPR, as I don't see any way in which Nexon would need the SSN for operating a business.
I think properly combatting hackers would probably require massive changes to the game engine and the game's system to make them much more difficult to mess with. After all, the game seems to be running on a quite old proprietary engine. Alternatively, if the base combat loop was made significantly more difficult (compensated with higher rewards of course) mobbing might be harder to automatize, though that might be a too radical change to the core gameplay itself.
I see your point and don't see a reason NOT to increase the maximum friend capacity, though I struggle to understand how you've managed to reach the current cap in a way that forces you to constantly delete existing friends.
I also doubt that one could manage hundreds of friends without issue, but that's neither here or there.