I think that's not quite the point. Leela has an advantage over AB chess engines, where it has multi-PV for "free", meaning it will evaluate multiple lines by default at no cost to performance (traditional engines, like Stockfish, will lose elo with multi-PV). This allows us to know at a glance if a position is "draw/win with perfect play" or if there is margin for error. If Leela shows multiple moves where one side maintains a winning advantage/losing disadvantage/equality, we can use that as a computer-based heuristic to know if a position is "easy" to play or not.
Yes and no – the number of playable lines does not necessarily tell us how "obvious" those lines are to find for a human.
To give a trivial example, if I take your queen, then recapturing my queen is almost always the single playable move. But it's also a line that you will easily find!
Conversely, in a complex tactical position, (even) multiple saving moves could all be very tricky for a human to calculate.
I wonder if there’s a combined metric that could be calculated. Depth of the line certainly would be impactful. A line that only works if you do 5 only moves is harder to find than a single move line. “Quiet” moves are probably harder to find than captures or direct attacks. Backwards moves are famously tricky to spot. Etc
And also, humans vary wildly in their thinking and what's "obvious" to them. I'm about 1950 and am good in openings and tactics (but not tactics for the opponent). Others around the same rating are much worse than that but they understand positional play much better - how to use weak squares, which pieces to exchange and so on. To me that's a kind of magic.
