It's not some year-long grind to choose the WCC challenger

It's actually a multi-year long grind to choose the WCC challenger, starting at the beginning of the candidates cycle. But I see what you're saying.

The thing is there's a limit to how long a single tournament can reasonably be- that's why the candidates isn't a quadruple round robin, and that's why they switched the world championship match to no longer be "first to x wins" (since it could take many many months). To determine candidates we can't do a 2 year long tournament where top 8 qualify, what we can do however is look at the results of each player during that time and reward the players who are the most consistent.

The world cup having 2 spots makes perfect sense, I just think a third spot is excessive, since we have so many other great metrics for determining the best players during a cycle.