Monero don't need any "serious investors" to be wildly successful. The black market alone is estimated to ~650 billion USD. If XMR only captures 1% of that market we're talking 6.5 billion usd, or split across 18.4 milion XMR that will give you a price of $353 per XMR. There's a calculator to play with the values here.

In reality it's hard to tell what would happen if 1% of the black market activity took place in XMR, but this could give us a ballpark figure, chances are it would be much higher.

So assuming your conclusion is true. A network by and for criminals could actually be a good thing, and I would be extremely bullish on a network as such. This is without even talking about tax havens where you'll find trillions in value. I think monero gaining traction in the dark web would be a great start and bootstrap it as a currency for criminals.