As VTC said, you do get some of your dilution fee back so it slightly helps your guys chances.
A dilution fee is fine, but the breakeven point shouldn´t be reached after several
months for a new investor if we assume that the site makes a profit. Of course
you can´t protect new investors from a downturn due to players running better then
expected.
Honestly, I'm not really sure that's a bad thing. I think the larger point is that any public bankroll system is always going to sort of hit an equilibrium of where people leave / don't invest because expected returns / risks are too unattractive for people to invest. There's some advantage in tweaking it such that the equilibrium is a bit higher (e.g. higher max profit) as well as disadvantages (e.g. more liability).
The way it is now, makes it more attractive for previous and long-term investors. I think that's pretty fair and reasonable. Obviously I'm pretty biased as a very early investors and any new investors disadvantage me due to dilution (although slightly compensate me for that with dilution fees).
But this misses the obvious fact that many investors
tend to gamble from time to time and investors going crazy (or simply trying to recoup
investment losses by gambling) has been the fuel for
a big percentage of site profits from time immemorial (the Just-Dice days

).
I've only thought about it for 30 seconds, so forgive me if I'm wrong. But in the current system investors can effectively borrow money against their bankroll investment, and then repay it (interest fee). Investors who wanted to gamble, could easily do that to gamble.
To borrow X money against your bankroll investment, just go "Onsite: -X, Offsite: +X" and then to repay the loan, do: "Onsite: +X, Offsite: -X" and you'll pay 0 fees (no dilution or interest!)
Maybe Daniel can make a simplified UI for "loans against your bankroll" rofl