A high score means your list is efficiently built. It does not mean you will win. A low score means the list is buying less raw capability per point than most — which is sometimes exactly right, if that is not what the list is for.
We could sell this harder than that. We would rather be the source that is still correct in a year.
What actually determines wins
Player skill dominates
At the top of any event, the lists are all reasonable. What separates first from fortieth is deployment, target priority, scoring discipline, knowing when to concede a phase, and not making the one mistake that loses the game on turn two. None of that is in your list file.
Matchups swing hard both ways
A list built to delete elite infantry meets a horde army and looks broken. The same list meets what it was built for and looks unstoppable. Its Battle Index is identical in both games. Real tournaments are five or six of these coin-flips stacked, and pairing decisions in team events stack them deliberately.
Missions and terrain decide games
The same two armies on different layouts play completely differently. Objective placement, sightlines, and which secondaries come up routinely matter more than raw efficiency.
Dice
Small samples. Six games is not a large sample.
And the field adapts
Lists that look inefficient on paper are often built to beat what is currently winning — which is a strategy the maths cannot see.
So what is the score for?
Efficiency is one input into winning, and it is the one input you can inspect and change before the event, at a desk, for free. That is worth knowing precisely. It is not worth overstating.