Here are some of my thoughts on uniqueness in GPPs.
Uniqueness doesn't matter at all. Ownership percentage matters -- but uniqueness is the wrong word for what matters about it. (And not just in the overly pedantic sense that uniqueness, like pregnancy, is strictly binary.)
The players you should be looking for are
under-owned players, and -- as Karlos Williams may demonstrate rather well -- under-ownedness and uniqueness are entirely different concepts.
Real DFS is complicated, so let's consider a simplified toy game to examine the relevant principle.
Suppose we have a 100-person contest with a tournament-style payout structure (you can make it winner-take-all for simplicity; it doesn't matter), and each lineup consists of a single player -- either the Broncos defense or the Raiders defense. Suppose the Broncos defense is a 2-1 favorite to outscore the Raiders defense, and suppose that 80% of the entrants will own the Broncos.
It is easy to see that the lineups with the Raiders will win money, on average, while the lineups with the Broncos will lose money. (Two-thirds of the time, 80% of the lineups will split the prize pool; one-third of the time, 20% of the lineups will split the prize pool. The latter group is the one that is +EV.)
The Raiders defense was more unique, and that's the one that was profitable. Does that mean that uniqueness is beneficial?
No. What made the Raiders defense profitable was that its 33% win rate was greater than its 20% ownership, and in that sense they were under-owned. But it's not at all the case that unique players are inherently under-owned while chalk players are inherently over-owned. Change the numbers from the example a bit -- make the broncos 7-1 favorites to outscore the Raiders rather than 2-1 favorites, and now it's the Broncos, at 80% ownership, that are under-owned while the Raiders, at 20%, are over-owned.
In general, uniqueness might be correlated with under-ownedness. That's an interesting empirical question that is worth looking into. But the correlation would not be perfect in any case, and there may be plenty of situations where 60%-owned guys might be under-owned because they are actually 70% likely to outscore similarly priced players at their position -- and that may well be the case with Karlos Williams this week.
See also: similar thoughts (but different in ways I'll elaborate on next week) from
Steve Buzzard and
John Lee.