Would a return to the n2 with a soft cap of ~1000mv solve enough problems to justify capping one account investment?

I don't think so.

Large investors could always have multiple accounts.

Sure but then they vote them together with a bot or something and we end up in the same place as before with very superlinear.

I don't know how much investment we get at different levels. It's pretty hard to measure especially given sock puppet account, stake moved between accounts, and such.