Sure. Where's the demonstration ? Here's mine :
What happens when you lack a role and there is not autofill :
1000 players starts to queue for a game, there are only 100 supports.
500 of the players find a match thanks to the 100 support.
500 players are still waiting.
1000 new players starts to queue they bring 100 new supports
you now have a total of 1500 players queuing (the 500 who were waiting + the 1000 new).
the 500 who were waiting are priorized and get matched with the 100 new supports.
1000 players are still waiting
1000 new players starts ...
...
1500 waiting ...
But now the 1500 waiting will have to wait until 3000 new players bring 300 new support to get matched. These 3000 new players will be waiting for 6000 new players to connect to bring 600 supports ....
Repeat until 10 000 players are waiting with 1h+ queue time.
Picking role before the game was a new feature, before that you had to respect pick order, everytime. So the system is better than before, and it NEEDS autofill, else it's not just the queue time will be longer, it's the queue time will GROW so much you wont even be able to play.