I probably phrased my explanation poorly: The queue doesn't need to be literally split in two for very similar behavior to take place as if it were split in too. In the end, you are further dividing an already small userbase along some preference.
In an ideal world, you could do this perfectly where you could input e.g. "I want a game with exactly 327 or less rating deviation" and then exactly get a game with such a deviation as fast as possible.
This is obviously impractical for many reasons and "get me a balanced game" or "get me any game asap" are preferences you can state, but are only fulfillable with everyone being satisfied if there are enough people on close enough to your end of the spectrum for a game, specifically a balanced game, to ever be found.
This is not the case for faf.
If we implemented such a slider, what will predictably happen is that either
- You have enough "fast game" players that they can find unbalanced games every couple minutes and the dozen or so "balanced game" players will literally never find a game, or
- You put players from the "balanced game" preference into unbalanced games, who will then probably just leave the game because they got literally the opposite of what they asked for.
Effectively you have split the queue in two even though, of course, a slider is technically gradual.
Not only is this all of this undesirable, this then gives rise to quite a few perverse incentives, because the slider states your preferences relative to other players: If you know that you will never get a game on the 100% "balanced" side of the slider, you want to be just slightly more on the unbalanced side than the other players looking for a "balanced" game, or you will predictably be excluded out of even most "balanced" games that you'd otherwise like to have played.
Such a slider would effectively be a crude voting system where strategic voting is the optimal choice, i.e. not stating your true preferences is optimal to achieve your prefered outcome.
Listen, I don't want to read 5 page long guides about the state of the "slider meta", the normal faf meta is already enough