1. The only good sites are the ones your potential mate is on. Size is a bigger feature than any you can design.
2. If your site sucks, then people get frustrated and everyone leaves. If your site is great, then people get paired off and everyone leaves.
Online dating doesn't just suffer from network effects, it suffers from second order network effects. Unless you're getting a constant stream of new customers into your site every day, your site will fail.
All innovation in online dating comes from the customer acquisition side, not the product side. If you manage to figure out an innovative new form of customer acquisition, you can make a go at creating a viable new entrant to the market. If you can't, it doesn't matter how good your product is, you will fail.