Product market fit and further growth are generally pretty correlated, though

Yes, but growth and appreciation are (theoretically) not. Growth is priced in. You're saying product-market fit -> growth -> appreciation. The first part of that is true. The second isn't. Assuming market efficiency, the VCs know just as well as I do that the company is going to grow, so they'll pay a higher rate, which means my options will be priced higher (or I'll get fewer RSUs, accordingly). Growth does not imply appreciation.

Assuming market efficiency at series B is quite a leap, IMO. That said, let's roll with that assumption; you need to find a company that continues to grow, or in some other way derisks itself.

This is like saying "To make money in the stock market, you have to find stocks that will go up." It's tautological.