If you're an early-stage investor you don't look for unicorns not because you don't want them (you obviously do) but because you can't spot them based on business model, traction, etc.
As an early stage investor you focus on team/founders because that's the best early predictor that a company will become a unicorn in the longer term.
I'm a little unclear on how the economics of seed-stage investors interlock with those of venture capitalists, and what level of influence VC decisions have over the whole ecosystem. But from the vantage point of a founder, modern seed stage investors seem like an unalloyed improvement.
According to people commenting here, it's not the team or founders, it's luck.
So you need a way to identify luck. Then you're golden!
The role of luck ("fortune", "fate") in the success of great people is a deep and ancient question, and you should not dismiss it. Machiavelli's Prince is at least 50% about the subject, and Sun Tzu is infatuated with it. Acknowledging luck does not mean dismissing the successful - it's just intellectual honesty.
Let's say there's some stochastic mechanics at work, randomness more than 'luck'. Luck is the attribute of someone, when randomness is an attribute of events, which makes a big difference.
Of course I can understand people citing 'luck' as necessary... but it's more superstition than science.
All in all, it means you can't really know for sure...
It's not exactly the same as a stochastic variable though. It's really any forces that you cannot influence, control, or anticipate.
Great team + great market = great business (for some definition of great, almost always < 1bn)
Great team + great market + luck = billion dollar business.